[C语言][LeetCode][167]Two Sum II - Input array is sorted

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本文介绍了一种解决TwoSumII问题的方法，即在已排序的整数数组中找到两个数，使它们的和等于特定的目标值。文章提供了一个C语言实现的例子，通过使用双指针技巧来高效地解决问题。

题目

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.

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

难度

中等

分析

题目意思是给定一个升序的整形数组，找到两个数字的和为target的，并返回下标。
解题思路是利用两个指针，一个指向头，一个指向末尾，然后比较这两个指针的和与target之间的大小。

C代码实现

int* twoSum(int* numbers, int numbersSize, int target, int* returnSize) {
    int * ret = (int *)malloc(sizeof(int));
    int i=0;
    int *p, *q;

    p = &numbers[0];
    q = &numbers[numbersSize-1];

    while(p != q)
    {
        if( (*p + *q) == target )
        {
            ret = (int *)realloc(ret, sizeof(int));
            ret[0] = (p-&numbers[0])+1;
            ret[1] = (q-&numbers[0])+1;
            *returnSize = 2;

            return ret;
        }
        else if( (*p + *q) > target )
            q = q -1;
        else if( (*p + *q) < target )
            p = p + 1;
    }

    *returnSize = 0;

    return NULL;
}