two sum problem
vector<int> twoSum(vector<int>& nums, int target) {
int front = 0, rear = nums.size() - 1;
sort(nums.begin(), nums.end());
while(front < rear) {
int sum = nums[front] + nums[rear];
if (sum == target)
break;
else if (sum > target)
rear--;
else
front++;
}
return {front, rear};
};