167. Two Sum II

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. Please note that 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.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

含义：在升序数组中，找到两个数，使其相加等于给定的目标值。注意索引位置是从1开始。

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