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.

思路：

一棵树是平衡二叉树，等价于两个子树都是平衡二叉树，并且两子树的深度差不超过1。

代码：

    int max(int a, int b){
        if(a > b)
            return a;
        return b;
    }
    int getDepth(TreeNode *root){
        if(root == NULL)
            return 0;
        if(root->left == NULL && root->right == NULL)
            return 1;
        return 1+max(getDepth(root->left), getDepth(root->right));
    }
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == NULL)
            return true;
        int d1 = getDepth(root->left), d2 = getDepth(root->right);
        if(d1 - d2 > 1 || d1 - d2 < -1)
            return false;
        return isBalanced(root->left)&&isBalanced(root->right);
    }