#leetcode#Longest Consecutive Sqeuence

最新推荐文章于 2022-03-06 23:29:26 发布

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本文探讨了如何在未排序的整数数组中找到最长连续整数序列的长度，通过构建图并使用DFS算法实现。重点在于算法的时间复杂度为O(n)，适合处理大规模数据集。

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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.

这题思路和word ladder有异曲同工之妙，都是抽象成图来用DFS，每个数字就是顶点，相邻数字之间有一条边， Code Ganker Rocks！

public class Solution {
    public int longestConsecutive(int[] nums) {
        if(nums == null || nums.length == 0)
            return 0;
        int res = Integer.MIN_VALUE;
        Set<Integer> set = new HashSet<Integer>();
        for(int i : nums){
            set.add(i);
        }
        while(!set.isEmpty()){
            Iterator iter = set.iterator();
            int item = (Integer)iter.next();
            set.remove(item);
            int len = 1;
            int i = item - 1;
            while(set.contains(i)){
                len++;
                set.remove(i--);
            }
            i = item + 1;
            while(set.contains(i)){
                len++;
                set.remove(i++);
            }
            res = Math.max(len, res);
        }
        return res;
    }
}