Description

Given an 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.

Return the indices of the two numbers (1-indexed) as an integer array answer of size 2, where 1 <= answer[0] < answer[1] <= numbers.length.

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

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.

Example 2:

Input: numbers = [2,3,4], target = 6
Output: [1,3]

Example 3:

Input: numbers = [-1,0], target = -1
Output: [1,2]

Constraints:

• 2 <= numbers.length <= 3 * 104
• 1000 <= numbers[i] <= 1000
• numbers is sorted in non-decreasing order.
• 1000 <= target <= 1000
• The tests are generated such that there is exactly one solution.

Solution

• 배열의 맨 앞과 뒤에 포인터를 하나씩 두고 두 값의 합이 타겟 값보다 크면 back--;, 작으면 front++;

public int[] twoSum(int[] numbers, int target) {
        if (numbers.length == 2) return numbers;
        int front = 0, back = numbers.length - 1;
        while (front < back) {
            if (numbers[front] + numbers[back] > target) back--;
            else if (numbers[front] + numbers[back] < target) front++;
            else return new int[]{front + 1, back + 1};
        }
        return null;
    }