LeetCode 1099. Two Sum Less Than K

原题链接在这里：https://leetcode.com/problems/two-sum-less-than-k/

题目：

Given an array A of integers and integer K, return the maximum S such that there exists i < j with A[i] + A[j] = S and S < K. If no i, jexist satisfying this equation, return -1.

Example 1:

Input: A = [34,23,1,24,75,33,54,8], K = 60
Output: 58
Explanation:
We can use 34 and 24 to sum 58 which is less than 60.

Example 2:

Input: A = [10,20,30], K = 15
Output: -1
Explanation:
In this case it's not possible to get a pair sum less that 15.

Note:

1. 1 <= A.length <= 100
2. 1 <= A[i] <= 1000
3. 1 <= K <= 2000

题解：

Sort the array. Use two pointers pointing at head and tail. Calculate the sum.

If sum < K, update res and l++ to increase sum.

Otherwise, r-- to decrease sum.

Time Complexity: O(nlogn). n = A.length.

Space: O(1).

AC Java:

 class Solution {
     public int twoSumLessThanK(int[] A, int K) {
         int res = -1;
         if(A == null || A.length == 0){
             return res;
         }
 
         Arrays.sort(A);
         int l = 0;
         int r  = A.length-1;
         while(l<r){
             int sum = A[l] + A[r];
             if(sum < K){
                 res = Math.max(res, sum);
                 l++;
             }else{
                 r--;
             }
         }
 
         return res;
     }
 }

类似Subarray Product Less Than K.