/*
	素数环问题
	2014-4-8 17:22:28
*/
#include <stdio.h>
#include <math.h>
#include <string.h>

bool hasSelected[21];
int site[21];

bool checkPrime(int k){
	if(k < 2) return 0;
	for(int i = 2; i <= sqrt(k); ++i)
		if(k % i == 0) return 0;
	return 1;
}

void print(){
	for(int i = 1; i < 21; ++i)
		printf("%d ", site[i]);
	printf("\n");
}

void backTrack(int k){
	if(k == 21){
		if(checkPrime(site[20] + site[1])) print();
		return;
	}
	int i, j;
	for(i = k; i < 21; ++i){
		for(j = 1; j < 21; ++j)
			if(!hasSelected[j] && checkPrime(j + site[k - 1])){ 
				site[k] = j; hasSelected[j] = 1; 
				backTrack(k + 1); hasSelected[j] = 0;
			}
	}
}

int main(){	
	//freopen( "data.out", "w", stdout );
	site[1] = 1;
	hasSelected[1] = 1;
	backTrack(2);
	return 0;
}

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MongoDB学习之旅二：安装及配置