solution(python): 1361. Validate Binary Tree Nodes

1361. Validate Binary Tree Nodes
- Python

Medium/1361. Validate Binary Tree Nodes/Readme.md

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+You have n binary tree nodes numbered from 0 to n - 1 where node i has two children leftChild[i] and rightChild[i], return true if and only if all the given nodes form exactly one valid binary tree.
+
+If node i has no left child then leftChild[i] will equal -1, similarly for the right child.
+
+Note that the nodes have no values and that we only use the node numbers in this problem.
+
+
+
+Example 1:
+
+
+Input: n = 4, leftChild = [1,-1,3,-1], rightChild = [2,-1,-1,-1]
+Output: true
+Example 2:
+
+
+Input: n = 4, leftChild = [1,-1,3,-1], rightChild = [2,3,-1,-1]
+Output: false
+Example 3:
+
+
+Input: n = 2, leftChild = [1,0], rightChild = [-1,-1]
+Output: false
+
+
+Constraints:
+
+n == leftChild.length == rightChild.length
+1 <= n <= 104
+-1 <= leftChild[i], rightChild[i] <= n - 1

Medium/1361. Validate Binary Tree Nodes/solution.py

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+class Solution:
+    def validateBinaryTreeNodes(self, n, leftChild, rightChild):
+        indegree = [0] * n  
+
+        for i in range(n):
+            if leftChild[i] != -1:
+                indegree[leftChild[i]] += 1
+            if rightChild[i] != -1:
+                indegree[rightChild[i]] += 1
+
+        root = None
+        for i in range(n):
+            if indegree[i] == 0:
+                if root is None:
+                    root = i
+                else:
+                    return False  
+
+        if root is None:
+            return False
+
+        visited = [False] * n
+        queue = deque([root])
+
+        while queue:
+            node = queue.popleft()
+            if visited[node]:
+                return False  
+            visited[node] = True
+            if leftChild[node] != -1:
+                queue.append(leftChild[node])
+            if rightChild[node] != -1:
+                queue.append(rightChild[node])
+
+        return sum(visited) == n