【Leetcode】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.

想法比较直接，就是先排序，然后慢慢去里面遍历找连续的element。

需要注意这么几点：

1.如果数组里只有1个元素，那么直接回复1.

2.一定要考虑duplicate的情况，因为比如排序后为1，1，1，2，3，一定要跳过重复的元素。

程序如下：

package testAndfun;import java.util.Arrays;public class LongestConsecutiveSequence {public static void main(String[] args){LongestConsecutiveSequence lcs = new LongestConsecutiveSequence();int[] input = {1,0,-1,1};System.out.println(lcs.longestConsecutive(input));}public int longestConsecutive(int[] num) {if(num.length<=1)return num.length;        int count =1 ;        int tmp=1;        Arrays.sort(num);                //System.out.println(Arrays.toString(num));        int i=0;        while(i<num.length-1){        if(num[i]==num[i+1]-1)tmp++;        if(num[i]==num[i+1]){        if(tmp>count){        count = tmp;        }        i++;        continue;        }        if(num[i]!=num[i+1]-1 || i==num.length-2){        if(tmp>count){        count = tmp;        }        tmp =1;        }        i++;        }        return count;    }}