LeetCode 167. Two Sum II - Input array is sorted

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本文介绍了一种在已排序的整数数组中寻找两个数使其和等于特定目标值的方法。通过使用双指针技术从两端逼近，可以高效地找到满足条件的两个数的索引。

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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

因为是有序的，所以只需要用两个指针分别从头尾进行检索，找到结果直接输出，若没有结果则直接输出异常。

    public int[] twoSum(int[] numbers, int target) {
        int[] result = new int[2];
        int i = 0;
        int j = numbers.length-1;
        while(i<j){
            int sum = numbers[i]+numbers[j];
            if(sum < target){
                i++;
            }
            else if(sum > target){
                j--;
            }
            else{
                result[0] = i + 1;
                result[1] = j + 1;
                return result;
            }
        }
        throw new IllegalArgumentException("1");
    }