【剑指Offer】51.构建乘积数组（Python实现）

题目描述

给定一个数组A[0,1,...,n-1],请构建一个数组B[0,1,...,n-1],其中B中的元素B[i]=A[0]*A[1]*...*A[i-1]*A[i+1]*...*A[n-1]。不能使用除法。（注意：规定B[0] = A[1] * A[2] * ... * A[n-1]，B[n-1] = A[0] * A[1] * ... * A[n-2];）

解法一：反向法

# -*- coding:utf-8 -*-
class Solution:
    def multiply(self, A):
        # write code here
        if not A:
            return []
        num = len(A)
        B = [None]*num
        B[0] = 1
        for i in range(1,num):
            B[i] = B[i-1]*A[i-1]
        temp = 1
        for i in range(num-2,-1,-1):
            temp *= A[i+1]
            B[i] *= temp
        return B