leetcode 543. Diameter of Binary Tree 最长树的片段 + 深度优先遍历DFS

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.

本题很简单就是在二叉树中寻找最长的片段，直接深度优先遍历即可

代码如下：

#include 
#include 
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#include 
#include 
#include 
#include 
#include 
#include 
#include 
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#include 
#include 

using namespace std;


/*
struct TreeNode 
{
     int val;
     TreeNode *left;
     TreeNode *right;
     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
 */

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

    int maxDepth(TreeNode* root, int& res)
    {
        if (root == NULL)
            return 0;
        else
        {
            int left = maxDepth(root->left,res);
            int right = maxDepth(root->right,res);
            res = max(res, left + right);
            return max(left, right) + 1;
        }
    }
};