2 Sum II.java

/*
Given an array of integers that is already sorted in ascending order, 
find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, 
where index1 must be less than index2.

Note:
Your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution and you may not use the same element twice.

Example:
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.


time = O(n)
space = O(1)
*/

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        if (numbers == null ||  numbers.length == 0) {
            return new int[]{};
        }
        int left = 0, right = numbers.length - 1;
        while (left < right) {
            if (numbers[left] + numbers[right] == target) {
                return new int[] {left + 1, right + 1};
            } else if (numbers[left] + numbers[right] < target) {
                left++;
            } else {
                right--;
            }
        }
        return new int[] {-1, -1};
    }
}