219. Contains Duplicate II

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 absolute difference between i and j is at most k.

在数组中找两个相等的数，如果他们索引之差的绝对值  <= k  则返回true

C++(26ms):

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_set<int> s ;
        int len = nums.size() ;
        for (int i = 0 ; i < len ; i++){
            if (i > k)
                s.erase(nums[i-k-1]) ;
            if (!s.insert(nums[i]).second)
                return true ;
        }
        return false ;
    }
};

C++（155ms）：

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int,int> Map ;
        int len = nums.size() ;
        bool flag = false ;
        for (int i = 0; i < len;i++ ){
            if (Map[nums[i]]){
                int t = abs(i+1 - Map[nums[i]]) ;          
                Map[nums[i]] = i+1 ;
                if (t <= k){
                    flag = true ;
                    break ;
                }   
            }else{
                Map[nums[i]] = i+1 ;
                cout<<Map[nums[i]]<<endl ;
            }
        }
        if (flag)
            return true ;
        else
            return false ;
        }
};