• 描述

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

• 分析

Two Sum的衍生版本，既然输入有序，那么在数组头尾各设一个指针，让他们往中间移动，如果相遇，那么就没有解，否则一定有解。

package leet.TwoSumII;

import java.util.HashMap;
import java.util.Map;

public class Solution {
    public static int[] getTwoSum(int[] arr, int target) {
        if(arr == null || arr.length < 2)
            return new int[]{0, 0};
        int low = 0, high = arr.length - 1;
        while(low < high) {
            int sum = arr[low] + arr[high];
            if(sum == target)
                return new int[]{low+1, high+1};
            else if(sum < target)
                ++low;
            else
                --high;
        }
        return new int[]{0, 0};
    }
}