UVa 524 - Prime Ring Problem（回溯）

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回溯法的简单应用。

#include<iostream>#include<cstdio>#include<string>#include<algorithm>#define MAXN 50using namespace std;int n, A[MAXN] = {1}, ispe[MAXN], vis[MAXN];void dfs(int cur) {    if(cur == n&& ispe[A[0] + A[n - 1]]) {        for(int i = 0; i < n; i++) {            i ? printf(" %d", A[i]) : printf("%d", A[i]);        }        printf("\n");    } else for(int i = 2; i <= n; i++) {        if(!vis[i]&& ispe[i + A[cur - 1]]) {            A[cur] = i;            vis[i] = 1;            dfs(cur + 1);            vis[i] = 0;        }    }}int main() {    for(int i = 2; i <= 50; i++)        ispe[i] = 1;    for(int i = 2; i <= 50; i++)        for(int j = i + i; j + i <= 50; j += i)            ispe[j] = 0;    int kase = 0;    while(cin >> n) {        if(kase++)            printf("\n");        printf("Case %d:\n", kase);        dfs(1);    }    return 0;}

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