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binaryTreeLongestConsecutiveSubsequence.java
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binaryTreeLongestConsecutiveSubsequence.java
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// 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).
// Example 1:
// Input:
// 1
// \
// 3
// / \
// 2 4
// \
// 5
// Output: 3
// Explanation: Longest consecutive sequence path is 3-4-5, so return 3.
// Example 2:
// Input:
// 2
// \
// 3
// /
// 2
// /
// 1
// Output: 2
// Explanation: Longest consecutive sequence path is 2-3, not 3-2-1, so return 2.
LOGIC, use DFS on tree updating a max, and we will increment our count, if next node value
is equal to target+1;
//TC: O(N) to go through all nodes
//SC: O(N) to store the nodes in stack
public class Solution {
private int max = 0; //can change this by passing in an arr of size 1, and updating it in helper,
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);
}
}