Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.
For example, given nums = [-2, 0, 1, 3], and target = 2.
Return 2. Because there are two triplets which sums are less than 2:
[-2, 0, 1] [-2, 0, 3]
Follow up:
Could you solve it in O(n2) runtime?
1 public class Solution { 2 public int ThreeSumSmaller(int[] nums, int target) { 3 if (nums == null || nums.Length < 3) return 0; 4 5 Array.Sort(nums); 6 7 int count = 0; 8 9 for (int i = 0; i < nums.Length - 2; i++) 10 { 11 int start = i + 1, end = nums.Length - 1; 12 13 while (start < end) 14 { 15 if (nums[i] + nums[start] + nums[end] < target) 16 { 17 count += end - start; 18 start++; 19 } 20 else 21 { 22 end--; 23 } 24 } 25 } 26 27 return count; 28 } 29 }