Leetcode-543-Diameter of Binary Tree

Leetcode-543-Diameter of Binary Tree

543. Diameter of Binary Tree

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• Total Accepted: 2826
• Total Submissions: 6539
• Difficulty: Easy
• Contributors: nagasupreeth

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.

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题解：

　　　面对树结构，常理采用recursion。 判断 左边 + 右边 是否最长， 回溯则选择最长的一边。

/**
 * 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 Search(TreeNode* root, int& ans){
        if(root->left==NULL && root->right==NULL){
            return 0; 
        }
        int lf = 0; 
        if(root->left){
            lf = Search(root->left, ans) + 1; 
        }
        int rg = 0; 
        if(root->right){
            rg = Search(root->right, ans) + 1; 
        }
        if(lf + rg > ans){
            ans = lf + rg; 
        }
        return max(lf,rg); 
    }

    int diameterOfBinaryTree(TreeNode* root) {
        int ans = 0; 
        if(root){
            Search(root, ans); 
        }
        return ans; 
    }
};