298. 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.

本题做的时候要想到DFS来解决，开始的思路是计算完一个自顶向下后统计一次最大值，但是看了答案后发现，可以每次计算完一个结点结算一次，用DFS的方法来遍历。由此可以了解dfs方法的视线