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.
Example 1:
Given the following tree [3,9,20,null,null,15,7]:
3
/ 9 20
/ 15 7
Return true.
Example 2:
Given the following tree [1,2,2,3,3,null,null,4,4]:
1
/ 2 2
/ 3 3
/ 4 4
Return false.
给定一个二叉树，判断是否高度平衡。高度平衡二叉树的定义：二叉树的任意节点的两个子树的深度差不超过1。
Python:
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution:
# @param root, a tree node
# @return a boolean
def isBalanced(self, root):
return (self.getHeight(root) >= 0)
def getHeight(self, root):
if root is None:
return 0
left_height, right_height = self.getHeight(root.left), self.getHeight(root.right)
if left_height < 0 or right_height < 0 or abs(left_height - right_height) > 1:
return -1
return max(left_height, right_height) + 1
C++:
class Solution {
public:
bool isBalanced(TreeNode *root) {
if (!root) return true;
if (abs(getDepth(root->left) - getDepth(root->right)) > 1) return false;
return isBalanced(root->left) && isBalanced(root->right);
}
int getDepth(TreeNode *root) {
if (!root) return 0;
return 1 + max(getDepth(root->left), getDepth(root->right));
}
};
C++:
class Solution {
public:
bool isBalanced(TreeNode *root) {
if (checkDepth(root) == -1) return false;
else return true;
}
int checkDepth(TreeNode *root) {
if (!root) return 0;
int left = checkDepth(root->left);
if (left == -1) return -1;
int right = checkDepth(root->right);
if (right == -1) return -1;
int diff = abs(left - right);
if (diff > 1) return -1;
else return 1 + max(left, right);
}
};
