Leetcode 128. Longest Consecutive Sequence

最新推荐文章于 2025-04-29 00:24:32 发布

原创最新推荐文章于 2025-04-29 00:24:32 发布 · 215 阅读

0 ·

CC 4.0 BY-SA版权

Leetcode 专栏收录该内容

51 篇文章

订阅专栏

本文介绍了一种寻找未排序整数数组中最长连续元素序列的算法，并提供了一个运行复杂度为O(n)的Java实现示例。该算法使用了Set集合来高效地查找连续序列。

Question

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

code

 /**
     * Set集合的办法
     * @param num
     * @return
     */
 public int longestConsecutive(int[] num) {
        if (num == null || num.length == 0) {
            return 0;
        }
        int max = 0;
        Set<Integer> sets = new HashSet<>();
        for (int i = 0; i < num.length; i++) {
            sets.add(num[i]);
        }
        for (int i = 0; i < num.length; i++) {
            int tempMax = 0;
            int t = num[i];
            while (sets.contains(t)) {
                sets.remove(t);
                t--;
                tempMax++;
            }
            t = num[i] + 1;
            while (sets.contains(t)) {
                sets.remove(t);
                t++;
                tempMax++;
            }
            max = Math.max(max, tempMax);
        }
        return max;
    }