//O(n) hashmaps C++ Two Sum leetcode
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
unordered_map<int,int> map;
for(int i=0; i<=nums.size();i++){
int compliment=target-nums[i];
if(map.count(compliment)==1){
return {map[compliment],i};
}
else{
map[nums[i]]=i;
}
}
return {-1,-1};
}
};