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.
Example:
Input: nums =[-2,0,1,3], and target = 2 Output: 2 Explanation: 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?
较小的三数之和。思路跟3sum差不多，但是这个题要找的是有多少种组合能满足三数之和小于target。思路还是先固定一个数字，然后另两个数字是通过双指针逼近的方式做。
时间O(n^2)
空间O(1)
Java实现
1 class Solution { 2 public int threeSumSmaller(int[] nums, int target) { 3 int res = 0; 4 Arrays.sort(nums); 5 for (int i = 0; i < nums.length - 2; i++) { 6 int left = i + 1; 7 int right = nums.length - 1; 8 while (left < right) { 9 if (nums[i] + nums[left] + nums[right] < target) { 10 res += right - left; 11 left++; 12 } else { 13 right--; 14 } 15 } 16 } 17 return res; 18 } 19 }
原文：https://www.cnblogs.com/cnoodle/p/12978028.html