HDU1016 DFS

Prime Ring Problem

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 40752    Accepted Submission(s): 18003

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

68

 

Sample Output

Case 1:1 4 3 2 5 61 6 5 2 3 4Case 2:1 2 3 8 5 6 7 41 2 5 8 3 4 7 61 4 7 6 5 8 3 21 6 7 4 3 8 5 2

再一次读错题目系列

#include <algorithm>#include <iostream>using namespace std;int num[30],book[30];int n;int p(int x){int i;for (i = 2; i <= sqrt(x+0.5); i++)if (x%i == 0)return 0;return 1;}void dfs(int x, int y){int i;for (i = 2; i <= n; i++){if (book[i] == 0){if (p(x + i)){book[i] = 1;num[y] = i;dfs(i, y + 1);book[i] = 0;}}}if (y == n + 1){if (p(x + 1)){for (i = 1; i<n; i++)printf("%d ", num[i]);printf("%d\n", num[n]);}}}int main(){int count = 1;while (scanf("%d", &n)!=EOF){printf("Case %d:\n", count++);num[1] = 1;book[1] = 1;dfs(1, 2);printf("\n");}return 0;}