package LeetCode_259 /** * 259. 3Sum Smaller * (Prime) * 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] * */ class Solution { /* * solution: sort array and two pointer, Time:O(n^2), Space:O(1) * */ fun threeSumSmaller(nums: IntArray, target: Int): Int { if (nums == null || nums.isEmpty()) { return 0 } nums.sort() var result = 0 val n = nums.size for (i in nums.indices) { var left = i + 1 var right = n - 1 while (left < right) { if (nums[i] + nums[left] + nums[right] < target) { /* * for example array is :1,2,..,..,5; target:9, if 1,2,5 is valid triplets, because array is sorted, * so the element at the left of 5(right pointer) and at the right of 2(left pointer) are all valid. * */ result += right - left left++ } else { right-- } } } return result } }