哈希表系列一＞存在重复元素II && 存在重复元素I

class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        Map<Integer,Integer> hash = new HashMap<>();//<nums[i],i>
        for(int i = 0; i < nums.length; i++){

            if(hash.containsKey(nums[i])){
               if(i - hash.get(nums[i]) <= k) return true; 
            }
            hash.put(nums[i],i);
        }
        return false;
    }
}

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Set<Integer> hash = new HashSet<>();
        for(Integer x : nums){
            if(hash.contains(x))
                return true;
            hash.add(x);    
        }
        return false;
    }
}