LeetCode563 Binary Tree Tilt

文章目录
  1. 1. 描述
  2. 2. 样例
  3. 3. 思路
  4. 4. 代码

描述

Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes’ tilt.

Note:

  1. The sum of node values in any subtree won’t exceed the range of 32-bit integer.
  2. All the tilt values won’t exceed the range of 32-bit integer.

样例

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Input: 
1
/ \
2 3
Output: 1
Explanation:
Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

思路

求二叉树的倾斜度。

一个节点的倾斜度是指:该节点 左子树所有节点值之和右子树所有节点值之和绝对差值

一棵树的倾斜度是指:该棵树所有节点的倾斜度之和

对二叉树dfs一遍即可求出答案

代码

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/**
* 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 ans = 0;
// 以root为根的子树所有节点值之和
int dfs(TreeNode* root) {
if (root == NULL) return 0;
int lsum = dfs(root->left), rsum = dfs(root->right);
// 添加节点root的倾斜度
ans += abs(lsum - rsum);
return lsum + rsum + root->val;

}
int findTilt(TreeNode* root) {
dfs(root);
return ans;
}
};
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