LeetCode 238

Product of Array Except Self

Given an array of n integers where n > 1, nums,
return an array output such that output[i] is equal to the product
of all the elements of nums except nums[i].

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up:
Could you solve it with constant space complexity?
(Note: The output array does not count as extra space
for the purpose of space complexity analysis.)

/*************************************************************************
    > File Name: LeetCode238.c
    > Author: Juntaran    
    > Mail: Jacinthmail@gmail.com
    > Created Time: 2016年04月28日 星期四 23时40分01秒
 ************************************************************************/

/*************************************************************************
    
    Product of Array Except Self
    
    Given an array of n integers where n > 1, nums, 
    return an array output such that output[i] is equal to the product 
    of all the elements of nums except nums[i].

    Solve it without division and in O(n).

    For example, given [1,2,3,4], return [24,12,8,6].

    Follow up:
    Could you solve it with constant space complexity? 
    (Note: The output array does not count as extra space 
    for the purpose of space complexity analysis.)

 ************************************************************************/
 
#include<stdio.h>

/**
 * Return an array of size *returnSize.
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* productExceptSelf(int* nums, int numsSize, int* returnSize)
{
    if( numsSize == 0 )
    {
        return 0;
    }

    int *result = malloc(numsSize*sizeof(int));
    *returnSize = numsSize;
    
    /* 从左往右 */
    int i;
    int leftProduct = 1;
    int rightProduct = 1;
    
    for( i=0; i<numsSize; i++ ){        
        result[i] = leftProduct;
        leftProduct *= nums[i];
    }
    /* 从右往左 */
    for( i = numsSize - 1; i>=0; i-- ){        
        result[i] *= rightProduct;
        rightProduct *= nums[i];
    }

    return result;
}

int main(){

    int nums[] = {1,2,3,4,5,6,7};
    int numsSize = 7;
    int returnSize[numsSize];
    productExceptSelf( nums, numsSize, returnSize);
    return 0;
}