[LeetCode] Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

这里要注意的是每个节点都要判断是否平衡，所以需要深搜下去。

int depth(TreeNode *node) {
    if (!node) return 0;
    if (!node->left) {
        return 1 + depth(node->right);
    }
    else if (!node->right) {
        return 1 + depth(node->left);
    }
    return 1+max(depth(node->left), depth(node->right));
}

bool isBalanced(TreeNode *root) {
    if (!root) return true;
    int val = depth(root->left) - depth(root->right);
    if (abs(val) <= 1) {
        return isBalanced(root->left) && isBalanced(root->right);
    }
    return false;
}