Untitled

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        map<int, int> ans;

        // key-> number , value -> last index it occured at

        for(int i= 0; i < nums.size(); i++){
            if( (ans.find(nums[i])!=ans.end()) && ( i-ans[nums[i]]<=k ) ){
                return true;
            }

            ans[nums[i]]=i;
        }


        return false;
    }
};