PROBLEM DESCRIPTION
Given the root of a binary tree, return the length of the longest consecutive sequence path. A consecutive sequence path is a path where the values increase by one along the path. Note that the path can start at any node in the tree, and you cannot go from a node to its parent in the path.
SOLUTION
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
int maxLength; // Initialize a variable to store the maximum length of consecutive sequence path.
public int longestConsecutive(TreeNode root) {
dfs(root); // Start the DFS traversal from the root node.
return maxLength; // Return the calculated maximum length.
}
public void dfs(TreeNode root) {
if (root == null) return; // If the current node is null, return (base case for recursion).
longestConsecutive(root.left); // Recursively traverse the left subtree.
helper(root); // Call the helper function to calculate the consecutive sequence length.
longestConsecutive(root.right); // Recursively traverse the right subtree.
}
public int helper(TreeNode root) {
if (root == null) return 0; // If the current node is null, return 0 (base case for recursion).
int left = 1; // Initialize a variable to store the length of consecutive sequence in the left subtree.
int right = 1; // Initialize a variable to store the length of consecutive sequence in the right subtree.
// Check if there is a consecutive sequence in the left subtree.
if (root.left != null && root.left.val == root.val + 1) {
left = 1 + helper(root.left); // Update the left length and recursively explore the left subtree.
}
// Check if there is a consecutive sequence in the right subtree.
if (root.right != null && root.right.val == root.val + 1) {
right = 1 + helper(root.right); // Update the right length and recursively explore the right subtree.
}
int currentLength = Math.max(left, right); // Calculate the current consecutive sequence length.
maxLength = Math.max(maxLength, currentLength); // Update the maximum length if necessary.
return currentLength; // Return the current consecutive sequence length.
}
}