标签：post ges bsp between present 分治 length repr private
同 563 Binary Tree Tilt 返回值是局部最大值, 需要全局变量
Given a binary tree, you need to compute the length of the diameter of the tree.
The diameter of a binary tree is the length of the longest path between any two nodes in a tree.
This path may or may not pass through the root. Example: Given a binary tree 1 / 2 3 / \ 4 5 Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3]. Note: The length of path between two nodes is represented by the number of edges between them.
分治: 后序遍历, 分治法返回到上一层时找到当前层的最大单子路径 . 全局变量看看本层的单子(左右子树)路径diameter 和是否大于全局变量来更新.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
int ans = 0;
public int diameterOfBinaryTree(TreeNode root) {
if (root == null) return 0;
helper(root);
return ans;
}
private int helper(TreeNode root) {
if (root == null) return 0;
if (root.left == null && root.right == null) return 1;
int left = helper(root.left);
int right = helper(root.right);
//Math.max函数保证不断在递归里进行更新ans的最大值
ans = Math.max(ans, left + right);
return Math.max(left, right) + 1;
}
}
标签：post ges bsp between present 分治 length repr private
原文地址：http://www.cnblogs.com/apanda009/p/7269985.html
