<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 {
private:
    bool solve(int node,vector<int> adj[],vector<int>& visited)
    {
        visited[node]=1;
        for(auto it:adj[node])
        {
            if(!visited[it])
            {
                if(solve(it,adj,visited)==false) return false;
            }
            else return false;
        }
        return true;
    }
public:
    bool validateBinaryTreeNodes(int n, vector<int>& leftChild, vector<int>& rightChild) {
        vector<int> adj[n];
        unordered_set<int> st;
        for(int i=0;i<n;i++)
        {
            int leftc=leftChild[i];
            int rightc=rightChild[i];
            if(leftc!=-1) 
            {
                adj[i].push_back(leftc);
                st.insert(leftc);
            }  
            if(rightc!=-1)
            {
                adj[i].push_back(rightc);
                st.insert(rightc);
            }
        }
        int node=-1;
        if(st.size()!=n-1) return false;
        else
        {
            for(int i=0;i<n;i++)
            {
                if(st.find(i)==st.end())
                {
                    node=i;
                    break;
                }
            }
        }
        vector<int> visited(n,0);
        if(solve(node,adj,visited)==false) return false;
        for(int i=0;i<n;i++)
        {
            if(!visited[i]) return false;
        }
        return true;
    }
};
51882