Count Univalue Subtrees

Source

• leetcode: 250

Given a binary tree, count the number of uni-value subtrees.

A Uni-value subtree means all nodes of the subtree have the same value.

For example:

Given binary tree,

    5
   / \
  1   5
 / \   \
5   5   5

return 4.

Java

public int countUnivalSubtrees(TreeNode root) {
    int[] count = new int[1];
    helper(root, count);
    return count[0];
}

private boolean helper(TreeNode node, int[] count) {
    if (node == null) {
        return true;
    }
    boolean left = helper(node.left, count);
    boolean right = helper(node.right, count);
    if (left && right) {
        if (node.left != null && node.val != node.left.val) {
            return false;
        }
        if (node.right != null && node.val != node.right.val) {
            return false;
        }
        count[0]++;
        return true;
    }
    return false;
}