LeetCode刷题【Array】 Product of Array Except Self

题目：

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 ofnums 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.)

解决方法一： Runtime:  2 ms

public class Solution {
    public int[] productExceptSelf(int[] nums) {
        if(null==nums) return null;
		int[] ret = new int[nums.length];
		for(int i=0;i<nums.length;i++) ret[i]=1;
		int sum=1;
		for(int i=1;i<nums.length;i++){
			sum*=nums[i-1];
			ret[i]=sum;
		}
		sum=1;
		for(int j=nums.length-2;j>=0;j--){
			sum*=nums[j+1];
			ret[j]*=sum;
		}
		return ret;
    }
}

参考：

【1】https://leetcode.com/