Prime Ring Problem，用 C 语言来计算

Question

Problem Description
A ring is compose of n circles as shown in diagram. Put natural number 1, 2, ..., n into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

Note: the number of first circle should always be 1.

Input
n (0 < n < 20).

Output
The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements. Print solutions in lexicographical order.

You are to write a program that completes above process.

Print a blank line after each case.

Sample Input
6
8

Sample Output
Case 1:
1 4 3 2 5 6
1 6 5 2 3 4

Case 2:
1 2 3 8 5 6 7 4
1 2 5 8 3 4 7 6
1 4 7 6 5 8 3 2
1 6 7 4 3 8 5 2

Answer 1

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#include<stdio.h>
#define MAX 20

int main(){
    int n;
    scanf("%d",&n);
    for(int i=1;i<=n;++i){
        for(int j=i;j>=1;j--){
            printf("%d ",j);
        }
        for(int k=n;k>=(n-i);--k--){
            printf("%d ",k);
        }
        printf("\n");
    }
    return 0;
}