https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/

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.

解题思路：

很简单，几乎没什么可说的。

对于已经排序的数组，two pointers分别指向头尾。

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int start = 0, end = numbers.length - 1;
        int[] res = new int[2];
        while (start < end) {
            if (numbers[start] + numbers[end] == target) {
                res[0] = start + 1;
                res[1] = end + 1;
                return res;
            } else if (numbers[start] + numbers[end] < target) {
                start++;
            } else {
                end--;
            }
        }
        return res;
    }
}

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.