167. Two Sum II - Input array is sorted

Posted 2022-11-24 Carl_Hugo

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. 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

解题思路：
设置两个指针，从两头扫描。因为数组有序，当两指针之和大于target则让后面的指针向前移动；当两指针之和小于target，则让前面的指针向后移动。

public class Solution 
    public int[] twoSum(int[] numbers, int target) 
        int end = numbers.length-1;
        int[] res = new int[2];
        for(int i=0,j=end;i<j;)
            if(numbers[i]+numbers[j]>target)
                j--;
            else if(numbers[i]+numbers[j]<target)
                i++;
            else
                res[0]=i+1;
                res[1]=j-1;
                break;
            
        
        return res;