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.

每个recursive 传入两个参数 一个记录上个root.val 另一个记录层数

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int max = 0;
    public int longestConsecutive(TreeNode root) {
        if(root == null)
            return 0;
        getMaxLen(root, 0, 0);
        return max;
    }
    public void getMaxLen(TreeNode root, int last, int cur){
        if(root == null) return;
        if(last+1 == root.val)
            cur++;
        else
            cur = 1;
        max = Math.max(max, cur);
        getMaxLen(root.left, root.val, cur);
        getMaxLen(root.right, root.val, cur);
    }
}