Binary Tree Longest Consecutive Sequence Leetcode

最新推荐文章于 2022-01-04 14:13:32 发布

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最新推荐文章于 2022-01-04 14:13:32 发布

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原文链接：http://www.cnblogs.com/aprilyang/p/6357883.html

解决寻找二叉树中最长连续路径的问题，通过递归方法实现。最长连续路径是指从父节点到子节点的路径，且节点值必须连续。

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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).

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.

感觉写这个题真的是千辛万苦。。。总觉得差一点就写出来了但是写了好久。。。

不过也许对recusive更了解一些了？谁知道呢。。。

整体思路就是设置一个全局变量记录当前的返回值即整体最优解，每次只返回连贯的局部最优解。

public class Solution {
    private int total = 0;
    public int longestConsecutive(TreeNode root) {
        helper(root);
        return total;
    }
    public int helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int max = 1;
        int left = helper(root.left);
        int right = helper(root.right);
        if (root.left != null && root.val == root.left.val - 1) {
            max = Math.max(left + 1, max);
        }
        if (root.right != null && root.val == root.right.val - 1) {
            max = Math.max(right + 1, max);
        }
        total = Math.max(max, total);
        return max;
    }
}