1. Two Sum
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
vector<int> ret;
unordered_map<int,int> mp;
for(int i = 0;i<nums.size();i++)
{
if(mp.count(target-nums[i])){
ret.push_back(mp[target-nums[i]]);
ret.push_back(i);
return ret;
}
else
{
mp[nums[i]] = i;
}
}
return ret;
}
};