#298. Binary Tree Longest Consecutive Sequence

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本文探讨了在二叉树中寻找最长连续序列路径的问题，通过递归算法遍历二叉树并更新最长连续序列，提供了详细的代码实现及示例说明。

题目描述：

Given a binary tree, find the length of the longest consecutive sequence path.

The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from parent to child (cannot be the reverse).

Example 1:

Input:

/ \

2 4

Output: 3

Explanation: Longest consecutive sequence path is 3-4-5, so return 3.

Example 2:

Input:

Output: 2

Explanation: Longest consecutive sequence path is 2-3, not 3-2-1, so return 2.

递归遍历二叉树，遍历的同时更新最长连续序列。

class Solution {
public:
    int longestConsecutive(TreeNode* root) {
        if(root==NULL) return 0;
        int max_length=1;
        max_length_from_cur(root,max_length);
        return max_length;
    }
    
    int max_length_from_cur(TreeNode* root, int& max_length)
    {
        if(root==NULL) return 0;
        int left=max_length_from_cur(root->left,max_length);
        int right=max_length_from_cur(root->right,max_length);
        int result=1;
        if(root->left!=NULL&&root->val==root->left->val-1) 
        {
            result=max(result,left+1);
            max_length=max(max_length,left+1);
        }
        if(root->right!=NULL&&root->val==root->right->val-1) 
        {
            result=max(result,right+1);
            max_length=max(max_length,right+1);
        }
        return result;
    }
};