219. Contains Duplicate II

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.

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

unordered_map<int, int> hash;

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

auto it = hash.find(nums[i]);
if (it!= hash.end() && i-it->second <= k)
return true;
else
hash[nums[i]]= i;//将<数值，下标>放入hash表中
}
return false;

}
};

class Solution {
public:
bool containsNearbyDuplicate(vector<int>& nums, int k) {
unordered_map<int,int> myMap;
for(int i = 0;i<nums.size();++i)
{
if(myMap.find(nums[i]) == myMap.end())
myMap[nums[i]] = i;
else
{
if(i-myMap[nums[i]] <=k)
return true;
else
myMap[nums[i]] = i;
}
}

return false;

}
};