Longest Consecutive Sequence（最长连续数值）_longest string of consecutive-优快云博客

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，并提供了一个运行在O(n)复杂度内的实现方案。通过使用HashSet数据结构来快速查找和删除元素，确保了算法效率。

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import java.util.HashSet;

/**
 * Longest Consecutive Sequence
 *
 * 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.
 */
public class LongestConsecutiveSequence {
    public static int getConsecutiveSequence(int[] arr) {
        if(null == arr || arr.length==0) {
            return 0;
        }
        HashSet<Integer> set = new HashSet<Integer>();
        for(int i : arr) {
            set.add(i);
        }
        int longest = 1;
        for(int i : arr) {
            if(!set.contains(i)){
                continue;
            }
            int length = 1;
            for(int j=i-1; set.contains(j); length++, j--){
                System.out.println(j);
                set.remove(j);
            }
            for(int j=i+1; set.contains(j); length++, j++){
                set.remove(j);
            }
            longest = Math.max(longest, length);
        }
        return longest;
    }
    public static void main(String[] arrs){
        int[] arr = {100, 4, 200, 1, 3, 2};
        int result = getConsecutiveSequence(arr);
        System.out.print(result);
    }
}