Likou question: 687. The longest path with the same value

Likou question: 687. The longest path with the same value

Given a binary tree, find the longest path, each node in this path has the same value. This path may or may not pass through the root node.

Note: The length of the path between two nodes is represented by the number of edges between them.

Example 1:

enter:

          5
         / \
        4   5
       / \   \
      1   1   5

Output:

2
Example 2:

enter:

          1
         / \
        4   5
       / \   \
      4   4   5

Output:

2

Source: LeetCode
Link: https://leetcode-cn.com/problems/longest-univalue-path
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Refer to the comment area @Jingfu's solution: java official solution thinking analysis: https://github.com/echofoo/ARTS/blob/master/A-20190925-longest path with the same value.md

/**
 * 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 ret;
    int get_maxlen(TreeNode* root){
    
    
        if (root == NULL){
    
    
            return 0;//叶子节点，返回0
        }
        int leftlen=get_maxlen(root->left);
        int rightlen=get_maxlen(root->right);
        int left=0,right=0; //当左右子树不相等的时候，不会进入if条件，将返回0
        if (root->right && root->val==root->right->val){
    
    
            right = rightlen+1;
        }
        if (root->left && root->val==root->left->val){
    
    
            left=leftlen+1;
        }
        ret = ret>left+right?ret:left+right;//如果递归回到根节点，那么这个就是我们最终需要的值
        return left>right?left:right;//返回左右子树中长度较长的一个分支
    }
    int longestUnivaluePath(TreeNode* root) {
    
    
        ret = 0;
        get_maxlen(root);
        return ret;
    }
};