我在一次工作面试中被问到这个问题,我想知道其他人是如何解决这个问题的。我最擅长使用Java,但也欢迎使用其他语言的解决方案。

给定一个数字数组nums,返回一个数字数组products,其中products[i]是所有nums[j]的乘积,j != i。 输入:[1,2,3,4,5] 输出:[(2 * 3 * 4 * 5),(1 * 3 * 4 * 5),(1 * 2 * 4 * 5),(1 * 2 * 3 * 5),(1 * 2 * 3 * 4)] = [120, 60, 40, 30, 24] 你必须在O(N)中不使用除法来做这个。


当前回答

    int[] arr1 = { 1, 2, 3, 4, 5 };
    int[] product = new int[arr1.Length];              

    for (int i = 0; i < arr1.Length; i++)
    {
        for (int j = 0; j < product.Length; j++)
        {
            if (i != j)
            {
                product[j] = product[j] == 0 ? arr1[i] : product[j] * arr1[i];
            }
        }
    }

其他回答

我们可以先从列表中排除nums[j](其中j != i),然后得到其余部分的乘积;下面是python解决这个难题的方法:

from functools import reduce
def products(nums):
    return [ reduce(lambda x,y: x * y, nums[:i] + nums[i+1:]) for i in range(len(nums)) ]
print(products([1, 2, 3, 4, 5]))

[out]
[120, 60, 40, 30, 24]
    int[] arr1 = { 1, 2, 3, 4, 5 };
    int[] product = new int[arr1.Length];              

    for (int i = 0; i < arr1.Length; i++)
    {
        for (int j = 0; j < product.Length; j++)
        {
            if (i != j)
            {
                product[j] = product[j] == 0 ? arr1[i] : product[j] * arr1[i];
            }
        }
    }

我们正在分解数组的元素,首先从下标之前开始,即前缀,然后是下标或后缀之后

class Solution:

   def productExceptSelf(nums):

      length = len(nums)


      result = [1] * length


      prefix_product = 1


      postfix_product = 1

# we initialize the result and products


      for i in range(length)

      result[i] *= prefix_product


       prefix_product *= nums[i]

#we multiply the result by each number before the index

      for i in range(length-1,-1,-1)

      result[i] *= postfix_product


      postfix_product *= nums[i]

#same for after index
   return result

抱歉,走路时用手机

下面是Ruby中的一行程序解决方案。

全国矿工工会。映射{|n| (num - [n]).inject(:*)}

def products(nums):
    prefix_products = []
    for num in nums:
        if prefix_products:
            prefix_products.append(prefix_products[-1] * num)
        else:
            prefix_products.append(num)

    suffix_products = []
    for num in reversed(nums):
        if suffix_products:
            suffix_products.append(suffix_products[-1] * num)
        else:
            suffix_products.append(num)
        suffix_products = list(reversed(suffix_products))

    result = []
    for i in range(len(nums)):
        if i == 0:
            result.append(suffix_products[i + 1])
        elif i == len(nums) - 1:
            result.append(prefix_products[i-1])
        else:
            result.append(
                prefix_products[i-1] * suffix_products[i+1]
            )
    return result