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。

思路

代码

import Strategy.Strategy;

import java.lang.reflect.Array;
import java.util.Arrays;

public class MultiArr {

    public static void main(String[] args){

        MultiArr multiArr = new MultiArr();
        int[] a = {1, 2, 3,4,5};
//        int[] a = {1,2};
        /*int[] a = {1, 2, 3,4,5,6};
        int[] a = {1, 2, 3,4,5,6};*/
        int[] multiply = multiArr.multiply(a);
        System.out.println(Arrays.toString(multiply));
    }
    public int[] multiply(int[] A) {
        //注意特殊case
        if(A.length == 0 || A == null)return A;
        if(A.length == 1) return A;

        int len = A.length;
        int[] B = new int[len];
        int[] C = new int[len];
        //设置数组C和D的初始值
        C[0] = 1;
        C[1] = A[0];
        int[] D = new int[len];
        D[len - 1] = 1;
        D[len - 2] = A[len - 1];
        //需要注意的就是两个for循环的边界条件
        for(int i = 1; i < len - 1; i++){
            C[i + 1] = C[i ] * A[i];
        }
        for(int i = len - 2; i >= 0; i--){
            D[i] = D[i+1] * A[i+1];
        }
        for(int i = 0; i < len; i++){
            B[i] = C[i] * D[i];
        }

        return B;

    }

}