[leetcode] Binary Tree Longest Consecutive Sequence


Binary Tree Longest Consecutive Sequence

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.

DFS, update result when backtracking.

/**
 * 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 longestConsecutive(TreeNode* root){
        int res = 0;
        _longestConsecutive(root, res);
        return res;
    }
    int _longestConsecutive(TreeNode* root, int& res) {
        if(root == nullptr) return 0;
        int leftLength, rightLength;
        leftLength = _longestConsecutive(root->left, res);
        rightLength = _longestConsecutive(root->right, res);
        int ans = 0;
        if(root->left && root->left->val == root->val + 1){
            ans = max(ans, leftLength + 1);
        }
        if(root->right && root->right->val == root->val + 1){
            ans = max(ans, rightLength + 1);
        }
        ans = max(ans, 1);
        res = max(res, ans);
        return ans;
    }
};

 

Leave a comment

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.