构建乘积数组

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。

import java.util.ArrayList;
public class Solution {
    
    //B[i]=A[0]*A[1]*...*A[i-1]*A[i+1]*...*A[n-1]
    //可以分成两部分计算
    //先计算： B[i]=A[0]*A[1]*...*A[i-1]
    //然后计算：B[i]*=A[i+1]*...*A[n-1]   
    public int[] multiply(int[] A) {
        int[] result = new int[A.length];
		int start = 1;
		for (int i = 0; i < A.length; i++) {
			result[i] = start;
			start *= A[i];
		}
		start = 1;
		for (int i = A.length - 1; i >= 0; i--) {
			result[i] *= start;
			start *= A[i];
		}
		return result;
    }
}