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Balanced Binary Tree.cpp
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Balanced Binary Tree.cpp
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/*
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.
Link: http://www.lintcode.com/en/problem/balanced-binary-tree/
Example: Given binary tree A={3,9,20,#,#,15,7}, B={3,#,20,15,7}
A) 3 B) 3
/ \ \
9 20 20
/ \ / \
15 7 15 7
The binary tree A is a height-balanced binary tree, but B is not.
Solution: We set when facing error, we return −1 to upper layer. And when the upper layer get −1, and we will know
that there is a error.
Source: None
*/
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
public:
/**
* @param root: The root of binary tree.
* @return: True if this Binary tree is Balanced, or false.
*/
bool isBalanced(TreeNode *root) {
// write your code here
if (root == nullptr) {
return true;
}
return helper(root) != -1;
}
int helper(TreeNode *root) {
if (root == nullptr) {
return 0;
}
int leftDepth = helper(root->left);
int rightDepth = helper(root->right);
if (leftDepth == -1 || rightDepth == -1 ||
abs(rightDepth - leftDepth) > 1) {
return -1;
}
return 1 + max(rightDepth, leftDepth);
}
};