LeetCode题解2.1.6

2.1.6 Longest Consecutive Sequence

描述

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

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

Your algorithm should run in O(n) complexity.

public static int solution2_1_6(int num[]){if(num.length==0)return 0;if(num.length==1)return 1;else{HashSet<Integer> tempSet=new HashSet<Integer>();for(int i=0;i<num.length;i++)tempSet.add(num[i]);int maxLen=1;for(int i=0;i<num.length;i++){int tempLen=1;int temp=num[i]+1;while(tempSet.contains(temp)){//对于HashSet可以在O（1）的时间复杂度内判断是否存在该元素tempSet.remove(temp);tempLen++;temp++;}temp=num[i]-1;while(tempSet.contains(temp)){tempSet.remove(temp);tempLen++;temp--;}if(tempLen>maxLen)maxLen=tempLen;if(tempLen>num.length)break;}return maxLen;}}