【LeetCode】298.Binary Tree Longest Consecutive Sequence(Medium)(加锁题)解题报告

【LeetCode】298.Binary Tree Longest Consecutive Sequence(Medium)(加锁题)解题报告

题目地址：https://leetcode.com/problems/binary-tree-longest-consecutive-sequence/
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).

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.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }

 time : O(n)
 space : O(n)
 */
class Solution {
    public int longestConsecutive(TreeNode root) {
        if(root == null) return 0;
        helper(root , 0,root.val);
        return res;
    }
    public void helper(TreeNode root,int max,int target){
        if(root == null) return;
        if(root.val == target){
            max++；
        }else max = 1;
        res = Math.max(res,max);
        helper(root.left,max,root.val+1);
        helper(root.right,max,root.val+1);
    }
}

Date：2018年3月17日