Binary Tree Tilt

最新推荐文章于 2025-03-24 11:27:32 发布

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本文介绍了一种通过后序遍历算法计算二叉树每个节点的倾斜值，并最终得出整棵树的总倾斜值的方法。文章详细解释了节点倾斜值的概念及其计算方式，同时提供了具体的实现代码。

题目描述：

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.

Example:

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

Note:

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

解题思路：

实际上是一个后序遍历，函数int postorder (TreeNode* node, int& res)中，res存放累加每一个节点的tilt，返回值是以当前节点为根时，子树所有节点的和。

代码：

class Solution {
public:
int findTilt(TreeNode* root) {
int res=0;
postorder(root,res);
return res;
}

int postorder (TreeNode* node, int& res)
{
if (node==NULL)
return 0;
int numl=postorder(node->left, res);
int numr=postorder(node->right, res);
res+=abs(numl-numr);
return numl+numr+node->val;
}
};