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

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

标签

Array、Two Pointers、Binary Search

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;
}