Two Sum (When Input Array is Sorted)

Problem Statement

Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length.

Return the indices of the two numbers, index1 and index2, added by one as an integer array [index1, index2] of length 2.

The tests are generated such that there is exactly one solution. You may not use the same element twice.

Your solution must use only constant extra space.

Method Signature

public static int[] twoSum(int[] numbers, int target)

Examples

Example 1:

Input: numbers = [2,7,11,15], target = 9

Output: [1,2]

Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 1, index2 = 2. We return [1, 2].

Example 2:

Input: numbers = [2,3,4], target = 6

Output: [1,3]

Explanation: The sum of 2 and 4 is 6. Therefore, index1 = 1, index2 = 3. We return [1, 3].

Example 3:

Input: numbers = [-1,0], target = -1

Output: [1,2]

Explanation: The sum of -1 and 0 is -1. Therefore, index1 = 1, index2 = 2. We return [1, 2].

Test Your Solution

import java.util.Arrays;

public class TwoSumIITest {
    public static void main(String[] args) {
        // Test cases
        int[] test1 = {2, 7, 11, 15};
        System.out.println(Arrays.toString(twoSum(test1, 9)));    // Expected: [1, 2]

        int[] test2 = {2, 3, 4};
        System.out.println(Arrays.toString(twoSum(test2, 6)));    // Expected: [1, 3]

        int[] test3 = {-1, 0};
        System.out.println(Arrays.toString(twoSum(test3, -1)));   // Expected: [1, 2]

        int[] test4 = {1, 2, 3, 4, 4, 9, 56, 90};
        System.out.println(Arrays.toString(twoSum(test4, 8)));    // Expected: [4, 5]

        int[] test5 = {5, 25, 75};
        System.out.println(Arrays.toString(twoSum(test5, 100)));  // Expected: [2, 3]
    }

    // Your implementation goes here
    public static int[] twoSum(int[] numbers, int target) {
        // TODO: Implement two sum for sorted array
        return new int[0];
    }
}