JZ-051 - Build an array of products

Build an array of products

Topic description

Given an array A[0,1,...,n-1], please construct an array B[0,1,...,n-1], where element B[i]=A[ 0] A[1] ... A[i-1] A[i+1] ... A[n-1]. Division cannot be used.

• (Note: Specify B[0] = A[1] A[2] ... A[n-1], B[n-1] = A[0] A[1] ... A[n-2];)
• For the case where A is of length 1, B is meaningless and cannot be constructed, so that case doesn't exist.

Topic link : Build a product array

code

/**
 * 标题：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。
 * （注意：规定B[0] = A[1] * A[2] * ... * A[n-1]，B[n-1] = A[0] * A[1] * ... * A[n-2];）
 * 对于A长度为1的情况，B无意义，故而无法构建，因此该情况不会存在。
 * 题目链接：
 * https://www.nowcoder.com/practice/94a4d381a68b47b7a8bed86f2975db46?tpId=13&&tqId=11204&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz51 {

    public int[] multiply(int[] A) {
        int n = A.length;
        int[] B = new int[n];
        for (int i = 0, product = 1; i < n; product *= A[i], i++) {       /* 从左往右累乘 */
            B[i] = product;
        }
        for (int i = n - 1, product = 1; i >= 0; product *= A[i], i--) {  /* 从右往左累乘 */
            B[i] *= product;
        }
        return B;
    }

    public static void main(String[] args) {
        Jz51 jz51 = new Jz51();
        int[] A = new int[]{1, 2, 3, 4, 5, 6};
        int[] result = jz51.multiply(A);
        for (int num : result) {
            System.out.print(num + " ");
        }
    }
}

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