leetcode 543. Diameter of Binary Tree

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于 2017-05-23 12:11:07 发布

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本文介绍了一种计算二叉树直径的有效方法。通过递归计算左右子树的长度，并将其和作为当前子树的最大直径，同时左右子树较长值加1作为当前子树的长度。最终得出整棵二叉树的最大直径。

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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 longestpath between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

求最大距离的两个节点。左右子树的长度之和为当前子树的最大Diameter，左右子树较大值+1为当前子树长度，递归求得整颗数的最大Diameter

/**
 * 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) {
        length(root);
        return ans;
    }
    
    private int length(TreeNode root){
        if(root==null) return 0;
        int left = length(root.left);
        int right = length(root.right);
        ans = Math.max(ans, left+right);
        return 1+Math.max(left, right);
    }
}