LeetCode-Contains Duplicate II

• Problem:

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i and jis at most k.(i和j的差最多是k)

• analysis:

利用HashMap比较容易想到，但是利用HashSet不好做，需要利用滑动游标标记，一旦end-start>k则删除HashSet的nums[start]项

• anwser:

1 

public class Solution {    public boolean containsNearbyDuplicate(int[] nums, int k) {        Map<Integer,Integer> map= new HashMap<Integer,Integer>();        int j;        for(int i=0;i<nums.length;i++){            if(map.containsKey(nums[i])){              j = map.get(nums[i]);               if((i-j)<=k) return true;              else {                  map.remove(nums[j]);                  map.put(nums[i],i);              }            }            else map.put(nums[i],i);        }        return false;    }}

2 

public class Solution {    public boolean containsNearbyDuplicate(int[] nums, int k) {         Set<Integer> appearedNum = new HashSet<Integer>();          int start = 0, end = 0;          for(int i = 0; i < nums.length; i++){              if(!appearedNum.contains(nums[i])){                  appearedNum.add(nums[i]);                  end++;              } else return true;              if(end - start  > k) {                  appearedNum.remove(nums[start]);                  start++;              }          }          return false;      }}