two sum problem
vector<int> twoSum(vector<int>& nums, int target) {
int len = nums.size();
for(int i = 0; i < len; i++) {
for(int j = i + 1; j < len; j++) {
if(nums[j] == target - nums[i])
return { i, j };
}
}
return {-1, -1};
};