Two Sum
https://leetcode.com/problems/two-sum/description/
class Solution {
public:
vector<int> twoSum(vector<int>& arr, int t) {
int n = arr.size();
unordered_map<int,int> um;
for(int i=0;i<n;i++){
if(um.count(t-arr[i])) {
return {i,um[t-arr[i]]};
}
else {
um[arr[i]] = i;
}
}
return {-1,-1};
}
};