Java
/**
549.Binary Tree Longest Consecutive Sequence II
Given a binary tree, you need to find the length of Longest Consecutive Path in Binary Tree.
Especially, this path can be either increasing or decreasing.
For example, [1,2,3,4] and [4,3,2,1] are both considered valid, but the path [1,2,4,3] is not valid.
On the other hand, the path can be in the child-Parent-child order, where not necessarily be parent-child order.
Example 1:
Input:
1
/ \
2 3
Output: 2
Explanation: The longest consecutive path is [1, 2] or [2, 1].
Example 2:
Input:
2
/ \
1 3
Output: 3
Explanation: The longest consecutive path is [1, 2, 3] or [3, 2, 1].
Note: All the values of tree nodes are in the range of [-1e7, 1e7].
@tag-tree
*/
public class Binary_Tree_Longest_Consecutive_Sequence_II {
class Solution {
public int longestConsecutive(TreeNode root) {
if (root == null) {
return 0;
}
int res = helper(root, 1) + helper(root, -1) + 1; // +1 is increasing, -1 is decreasing
return Math.max(res, Math.max(longestConsecutive(root.left), longestConsecutive(root.right)));
}
int helper(TreeNode node, int diff) {
if (node == null) {
return 0;
}
int left = 0, right = 0;
if (node.left != null && node.val - node.left.val == diff) {
left = 1 + helper(node.left, diff);
}
if (node.right != null && node.val - node.right.val == diff) {
right = 1 + helper(node.right, diff);
}
return Math.max(left, right);
}
}
}