# [LeetCode] Binary Tree Longest Consecutive Sequence

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Problem Description:

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).

For example,

   1
\
3
/ \
2   4
\
5


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

   2
\
3
/
2
/
1


Longest consecutive sequence path is 2-3,not3-2-1, so return 2.

This post shares an elegant C++ solution, just in 4 lines. The code is as follows.

 1 /**
2  * Definition for a binary tree node.
3  * struct TreeNode {
4  *     int val;
5  *     TreeNode *left;
6  *     TreeNode *right;
7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
8  * };
9  */
10 class Solution {
11 public:
12     int longestConsecutive(TreeNode* root) {
13         return longest(root, NULL, 0);
14     }
15 private:
16     int longest(TreeNode* now, TreeNode* parent, int len) {
17         if (!now) return len;
18         len = (parent && now->val == parent->val + 1) ? len + 1 : 1;
19         return max(len, max(longest(now->left, now, len), longest(now->right, now, len)));
20     }
21 };

995 0
[LeetCode] Binary Tree Zigzag Level Order Traversal
To be honest, I do not know whether this problem is designed to let you use stacks. Anyway, I don't. Here are my codes, both BFS and DFS version.
555 0
[LeetCode] Longest Consecutive Sequence
This problem is not very intuitive at first glance. However, the final idea should be very self-explanatory.
584 0
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