Binary Tree Longest Consecutive Sequence

Source

• leetcode: 298

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.

Java

private int max = 0;
public int longestConsecutive(TreeNode root) {
    if(root == null) return 0;
    helper(root, 0, root.val);
    return max;
}

public void helper(TreeNode root, int cur, int target){
    if(root == null) return;
    if(root.val == target) cur++;
    else cur = 1;
    max = Math.max(cur, max);
    helper(root.left, cur, root.val + 1);
    helper(root.right, cur, root.val + 1);
}