用遞歸來解題。
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool isBalanced(TreeNode* root) {
return nextLevel(root, 0) >= 0;
}
int nextLevel(TreeNode* root, int level) {
if (!root) return level;
int ld = nextLevel(root->left, level + 1);
if (ld < 0) return -1;
int rd = nextLevel(root->right, level + 1);
if (rd < 0) return -1;
if (abs(ld - rd) > 1) return -1;
return ld > rd ? ld : rd;
}
};