Leetcode Binary Tree Longest Consecutive Sequence

最新推荐文章于 2021-01-10 11:47:19 发布

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最新推荐文章于 2021-01-10 11:47:19 发布

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本文介绍了一种算法，用于寻找给定二叉树中最长连续序列路径的长度。该路径必须从父节点到子节点，不可逆。通过示例说明了如何实现这一目标，并提供了具体的代码实现。

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,

Longest consecutive sequence path is 3-4-5, so return 3.

Longest consecutive sequence path is 2-3,not3-2-1, so return 2.

Difficulty: Medium

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