Binary Tree Longest Consecutive Sequence Leetcode

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.

 

感觉写这个题真的是千辛万苦。。。总觉得差一点就写出来了但是写了好久。。。

不过也许对recusive更了解一些了？谁知道呢。。。

整体思路就是设置一个全局变量记录当前的返回值即整体最优解，每次只返回连贯的局部最优解。

public class Solution {
    private int total = 0;
    public int longestConsecutive(TreeNode root) {
        helper(root);
        return total;
    }
    public int helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int max = 1;
        int left = helper(root.left);
        int right = helper(root.right);
        if (root.left != null && root.val == root.left.val - 1) {
            max = Math.max(left + 1, max);
        }
        if (root.right != null && root.val == root.right.val - 1) {
            max = Math.max(right + 1, max);
        }
        total = Math.max(max, total);
        return max;
    }
}

不知道下次还能不能一下写出来，以后回顾一下吧。。。

没用top solution写一遍，有心情再写吧。。。我觉得我的方法也挺好的哈哈哈