leetcode 543. Diameter of Binary Tree

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.

题目大意：求二叉树中任意两点的最长路径长度。

思路：分别求当前结点的左子树深度和右子树深度。将其相加得到x，并保留x的最大值。

/**
* 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 Max = 0;
int dfs(TreeNode* root) {
if (root == nullptr) return 0;
int d1 = 0;
int d2 = 0;
d1 = dfs(root->left);
++d1;
d2 = dfs(root->right);
++d2;
Max = max(d1 + d2 - 2, Max);
return max(d1, d2);
}
int diameterOfBinaryTree(TreeNode* root) {
dfs(root);
return Max;
}
};