<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:
    vector<int> vis;

    bool dfs(int u, vector<int> &lefc, vector<int> &rc){
        if(u == -1)return false;
        if(vis[u])return true;
        vis[u] = 1;
        return dfs(lefc[u], lefc, rc) || dfs(rc[u], lefc, rc);
    }

    bool validateBinaryTreeNodes(int n, vector<int> &leftChild, vector<int> &rightChild)
    {
        vector<int> indegree(n);

        vector<int> par(n, -1);
        for (int i = 0; i < n; i++)
        {
            if (leftChild[i] != -1)
            {
                indegree[leftChild[i]]++;
                
                if (par[leftChild[i]] != -1)
                    return false;
                par[leftChild[i]] = i;
            }
            if (rightChild[i] == -1)
                continue;
            indegree[rightChild[i]]++;
            if (par[rightChild[i]] != -1)
                return false;
            par[rightChild[i]] = i;
        }

        int t = 0;
        int root = -1;
        for (int a : par)
        {
            if (a == -1)
            {
                t++;
                root = a;
            }

            else
            {
                int lc = leftChild[a];
                int rc = rightChild[a];
                if (lc != -1)
                {
                    if (leftChild[lc] == a || rightChild[lc] == a)
                        return false;
                }
                if (rc != -1)
                {
                    if (leftChild[rc] == a || rightChild[rc] == a)
                        return false;
                }
            }

            // cout<<a<<endl;
        }


        if(t != 1)return false;
        unordered_set<int> myset;
        queue<int> q;
        for(int i= 0; i<n; i++){
            if(indegree[i] == 0){
                q.push(i);
                // myset.insert(i);
            }
        }
        while(q.size()){
            int f = q.front();
            q.pop();
            int lc = leftChild[f];
            int rc = rightChild[f];
            myset.insert(f);
            if(lc != -1){
                if(--indegree[lc] == 0){
                    q.push(lc);
                }
                
            }
            if(rc != -1){
                if(--indegree[rc] == 0){
                    q.push(rc);
                }
            }
        }
        // return true;
        return myset.size() == n;


        
    }
};
41172