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.)

 

 1 /*************************************************************************
 2     > File Name: LeetCode238.c
 3     > Author: Juntaran    
 4     > Mail: Jacinthmail@gmail.com
 5     > Created Time: 2016年04月28日 星期四 23时40分01秒
 6  ************************************************************************/
 7 
 8 /*************************************************************************
 9     
10     Product of Array Except Self
11     
12     Given an array of n integers where n > 1, nums, 
13     return an array output such that output[i] is equal to the product 
14     of all the elements of nums except nums[i].
15 
16     Solve it without division and in O(n).
17 
18     For example, given [1,2,3,4], return [24,12,8,6].
19 
20     Follow up:
21     Could you solve it with constant space complexity? 
22     (Note: The output array does not count as extra space 
23     for the purpose of space complexity analysis.)
24 
25  ************************************************************************/
26  
27 #include<stdio.h>
28 
29 /**
30  * Return an array of size *returnSize.
31  * Note: The returned array must be malloced, assume caller calls free().
32  */
33 int* productExceptSelf(int* nums, int numsSize, int* returnSize)
34 {
35     if( numsSize == 0 )
36     {
37         return 0;
38     }
39 
40     int *result = malloc(numsSize*sizeof(int));
41     *returnSize = numsSize;
42     
43     /* 从左往右 */
44     int i;
45     int leftProduct = 1;
46     int rightProduct = 1;
47     
48     for( i=0; i<numsSize; i++ ){        
49         result[i] = leftProduct;
50         leftProduct *= nums[i];
51     }
52     /* 从右往左 */
53     for( i = numsSize - 1; i>=0; i-- ){        
54         result[i] *= rightProduct;
55         rightProduct *= nums[i];
56     }
57 
58     return result;
59 }
60 
61 int main(){
62 
63     int nums[] = {1,2,3,4,5,6,7};
64     int numsSize = 7;
65     int returnSize[numsSize];
66     productExceptSelf( nums, numsSize, returnSize);
67     return 0;
68 }

 

posted @ 2016-04-29 03:39  Juntaran  阅读(237)  评论(0)  编辑  收藏  举报