LeetCode 128 Longest Consecutive Sequence

最新推荐文章于 2022-07-02 13:46:24 发布

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本文介绍了一种寻找整数数组中最长连续元素序列的算法。该算法通过使用HashSet数据结构达到O(n)的时间复杂度，举例说明了如何找到[100,4,200,1,3,2]中的最长连续序列[1,2,3,4]并返回其长度4。

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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.

Runtime: 11 ms

	public int longestConsecutive(int[] nums) {
		Set<Integer> set = new HashSet<>();
		for (int n : nums) set.add(n);
		int max = 0;
		for (int n : set) {
			if (!set.contains(n - 1)) {  // only check for one direction
				int m = n + 1;
				while (set.contains(m)) {
					m++;
				}
				max = Math.max(max, m - n);
			}
		}
		return max;
	}

常用数据结构及复杂度