3Sum Smaller.cpp

class Solution {
public:
   int threeSumSmaller(vector<int>& nums, int target) {
      int len = nums.size(), res = 0;
      if (len < 3)return 0;
      sort(nums.begin(), nums.end());
      for (int i = 0; i + 2 < len; ++i)
      {
         int lo = i + 1, hi = len - 1;
         while (lo < hi)
         {
            int sum = nums[i] + nums[lo] + nums[hi];
            if (sum >= target)
               --hi;
            else
            {
               res += hi - lo;
               ++lo;
            }
         }
      }
      return res;
   }
};