<p>You have <code>n</code> binary tree nodes numbered from <code>0</code> to <code>n - 1</code> where node <code>i</code> has two children <code>leftChild[i]</code> and <code>rightChild[i]</code>, return <code>true</code> if and only if <strong>all</strong> the given nodes form <strong>exactly one</strong> valid binary tree.</p>

<p>If node <code>i</code> has no left child then <code>leftChild[i]</code> will equal <code>-1</code>, similarly for the right child.</p>

<p>Note that the nodes have no values and that we only use the node numbers in this problem.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/08/23/1503_ex1.png" style="width: 195px; height: 287px;" />
<pre>
<strong>Input:</strong> n = 4, leftChild = [1,-1,3,-1], rightChild = [2,-1,-1,-1]
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/08/23/1503_ex2.png" style="width: 183px; height: 272px;" />
<pre>
<strong>Input:</strong> n = 4, leftChild = [1,-1,3,-1], rightChild = [2,3,-1,-1]
<strong>Output:</strong> false
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/08/23/1503_ex3.png" style="width: 82px; height: 174px;" />
<pre>
<strong>Input:</strong> n = 2, leftChild = [1,0], rightChild = [-1,-1]
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == leftChild.length == rightChild.length</code></li>
	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
	<li><code>-1 &lt;= leftChild[i], rightChild[i] &lt;= n - 1</code></li>
</ul>

class Solution {
    public:
        bool ans = 1;
            vector<int> topo(int V, vector<int> adj[],vector<int>&ans) 
            	{
                	    vector<int>indeg(V,0);
                        	    for(int i = 0; i < V; i++){
                                	        for(auto x : adj[i]){
                                            	            indeg[x]++;
                                                            	        }
                                                                        	    }
                                                                                	    queue<int>q;
                                                                                        	    for(int i = 0; i < V ;i++){
                                                                                                	        if(indeg[i] == 0){
                                                                                                            	            q.push(i);
                                                                                                                            	        }
                                                                                                                                        	    }
                                                                                                                                                	    while(!q.empty()){
                                                                                                                                                        	        int node = q.front();
                                                                                                                                                                    	        q.pop();
                                                                                                                                                                                	        ans.push_back(node);
                                                                                                                                                                                            	        
                                                                                                                                                                                                        	        for(auto x : adj[node]){
                                                                                                                                                                                                                    	            indeg[x]--;
                                                                                                                                                                                                                                    	            if(indeg[x] == 0) q.push(x);
                                                                                                                                                                                                                                                    	        }
                                                                                                                                                                                                                                                                	        
                                                                                                                                                                                                                                                                            	    }
                                                                                                                                                                                                                                                                                    	    return ans;
                                                                                                                                                                                                                                                                                            	}

                                                                                                                                                                                                                                                                                                    void dfs(int ind,vector<int> &vis,vector<int> adj[]){
                                                                                                                                                                                                                                                                                                            vis[ind] = 1;

                                                                                                                                                                                                                                                                                                                    for(int i = 0; i < adj[ind].size(); i++){
                                                                                                                                                                                                                                                                                                                                if(!vis[adj[ind][i]]){
                                                                                                                                                                                                                                                                                                                                                dfs(adj[ind][i], vis, adj);
                                                                                                                                                                                                                                                                                                                                                            }else{
                                                                                                                                                                                                                                                                                                                                                                            ans = 0;
                                                                                                                                                                                                                                                                                                                                                                                        }
                                                                                                                                                                                                                                                                                                                                                                                                }
                                                                                                                                                                                                                                                                                                                                                                                                    }
                                                                                                                                                                                                                                                                                                                                                                                                        bool validateBinaryTreeNodes(int n, vector<int>& leftChild, vector<int>& rightChild) {
                                                                                                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                                                                                                        vector<int> adj[n];
                                                                                                                                                                                                                                                                                                                                                                                                                                vector<int> topoSort;
                                                                                                                                                                                                                                                                                                                                                                                                                                        for(int i = 0; i < n ;i++){
                                                                                                                                                                                                                                                                                                                                                                                                                                                    if(leftChild[i] != -1)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                adj[i].push_back(leftChild[i]);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                            if(rightChild[i] != -1)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        adj[i].push_back(rightChild[i]);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                }

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        topo(n,adj,topoSort);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                if(topoSort.size() != n)return false;

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        vector<int>vis(n,0);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                int ct = 0;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        for(auto x: topoSort)cout<<x<<" ";

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                for(int i = 0; i < topoSort.size(); i++){
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            if(!vis[topoSort[i]]){
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            dfs(topoSort[i] ,vis ,adj);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            ct ++;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        cout<<ct <<endl;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                if(ct > 1)return false;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        return ans;

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            };

45897