LeetCode 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.)

题意：给出一个数组，求数组中除去其中一个数的乘积

思路：用left[i]表示i左边数的乘积,right[i]表示i右边数的乘积，则output[i] = left[i] *right[i],可以进一步优化，先用output[i]计算出left[i]

代码如下

public class Solution
{
public int[] productExceptSelf(int[] nums)
{
int len = nums.length;
int[] ans = new int[len];

for (int i = 0, tmp = 1; i < len; i++)
{
ans[i] = tmp;
tmp *= nums[i];
}

for (int i = len - 1, tmp = 1; i >= 0; i--)
{
ans[i] *= tmp;
tmp *= nums[i];
}

return ans;
}
}