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.

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.

用two pointer

时间：O(N), 空间：O(1)

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int l = 0, r = numbers.length - 1;
        while(l < r) {
            if(numbers[l] + numbers[r] > target)
                r--;
            else if(numbers[l] + numbers[r] < target)
                l++;
            else
                break;
        }
        return new int[] {l + 1, r + 1};
    }
}