leetcode 110 Balanced Binary Tree(DFS)
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.
题意:给一棵二叉树,判断它是否是平衡二叉树(即每个节点的左右子树深度之差不大于1).
题解:dfs的简单应用。有一个技巧是:用返回-1来表示不行。
/**
* 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:
int dfs(TreeNode *r){
if(r==NULL){
return ;
}
int ll=dfs(r->left);
int rr=dfs(r->right);
if(rr==-||ll==-||abs(ll-rr)>){
return -;
}
else{
return max(ll,rr)+;
}
}
bool isBalanced(TreeNode* root) {
if(dfs(root)==-){
return false;
}
else{
return true;
}
}
};
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