Given an array of integers and an integer k,
find out whether there there are two distinct indices i and j in
the array such that nums[i] = nums[j] and
the difference between iand j is
at most k.

哈希表的使用

class Solution {

public:

    bool containsNearbyDuplicate(vector<int>& nums, int k) {

        map<int,int> value;

    	for(int i=0;i<nums.size();++i)

    	{

    		if(value.find(nums[i])!=value.end()  &&  i-value[nums[i]]<=k)

    			return true;

    		value[nums[i]]=i;

    	}

    	return false;

    }

};