259. 3Sum Smaller

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.

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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

Constraints:

n == nums.length
0 <= n <= 3500
-100 <= nums[i] <= 100
-100 <= target <= 100

Solution

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class Solution {

    public int threeSumSmaller(int[] nums, int target) {
        Arrays.sort(nums);
        int n = nums.length;
        int count = 0;
        for (int i = 0; i < n - 2; i++) {
            int lo = i + 1;
            int hi = n - 1;
            while (lo < hi) {
                int sum = nums[i] + nums[lo] + nums[hi];
                if (sum < target) {
                    count += hi - lo;
                    lo++;
                } else {
                  hi--;
                }
            }
        }
        return count;
    }
}

Solution#

Solution