Question

Formatted question description: https://leetcode.ca/all/1099.html

 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, j, exist 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 <= A.length <= 100
     1 <= A[i] <= 1000
     1 <= K <= 2000

Algorithm

(brute force) O(n^2)

Enumerate i and j, and then find the maximum value less than K.

time complexity

Two-level loop traversal, so the time complexity is O(n^2)).

Space complexity

Only a constant number of traversals are needed, so the space complexity is O(1).

Code

Java

import java.util.Arrays;


public class Two_Sum_Less_Than_K {
    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;
        }
    }
}

// OJ: https://leetcode.com/problems/two-sum-less-than-k/
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int twoSumLessThanK(vector<int>& A, int k) {
        sort(begin(A), end(A));
        int i = 0, j = A.size() - 1, ans = INT_MIN;
        while (i < j) {
            int sum = A[i] + A[j];
            if (sum < k) {
                ans = max(ans, sum);
                ++i;
            } else --j;
        }
        return ans == INT_MIN ? -1 : ans;
    }
};

class Solution:
    def twoSumLessThanK(self, nums: List[int], k: int) -> int:
        nums.sort()
        low, high = 0, len(nums) - 1
        res = -1
        while low < high:
            val = nums[low] + nums[high]
            if val < k:
                res = max(res, val)
                low += 1
            else:
                high -= 1
        return res

1099 - Two Sum Less Than K

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