[leetcode]259. 3Sum Smaller 三数之和小于目标值

Given an array of n integers nums and an integer 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.

Follow up: Could you solve it in O(n2) runtime?

 

Example 1:

Input: nums = [-2,0,1,3], target = 2
Output: 2
Explanation: Because there are two triplets which sums are less than 2:
[-2,0,1]
[-2,0,3]

Example 2:

Input: nums = [], target = 0
Output: 0

Example 3:

Input: nums = [0], target = 0
Output: 0

 

题意

三数之和小于target的个数

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思路

K Sum 模板

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代码

 public int threeSumSmaller(int[] nums, int target) {
        if (nums == null || nums.length == 0) return 0;
        int result = 0;
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            int j = i + 1;
            int k = nums.length - 1;
            while (j < k) {
                int sum = nums[i] + nums[j] + nums[k];
                if (sum < target) {
                    result += k - j;
                    j++;
                } else {
                    k--;
                }
            }
        }
        return result;
    }