POJ-2034 Anti-prime Sequences dfs

筛出素数然后直接暴力即可。

代码如下：

#include <cstdlib>

#include <cstring>

#include <cstdio>

#define MAXN 10000

using namespace std;



int N, M, d, p[600005];

int hash[10005], path[10005];



void pre()

{

    int k;

    for (int i = 4; i <= MAXN; i += 2) {

        p[i] = 1;

    }    

    for (int i = 3; i <= 105; i += 2) {

        if (!p[i]) {

            k = 2 * i;     

            for (int j = i * i; j <= MAXN; j += k) {

                p[j] = 1;

            }

        }

    }

}



bool dfs(int x, int step)

{

    path[step] = x;

    if (step >= 2) { 

        int sum = path[step], k = step > d ? d : step;

        for (int i = step-1; i > step-k; --i) {

            sum += path[i];

            if (!p[sum]) {

                return false;

            }

        }

        if (step == M-N+1) {

            for (int i = 1; i <= M-N+1; ++i) {

                printf(i == 1 ? "%d" : ",%d", path[i]);

            }

            puts("");

            return true;

        }

    }

    for (int i = N; i <= M; ++i) {

        if (!hash[i]) {

            hash[i] = 1;

            if (dfs(i, step + 1)) {

                return true;

            }

            hash[i] = 0;

        }

    }

    return false;

}



int main()

{

    int flag;

    pre(); 

    while (scanf("%d %d %d", &N, &M, &d), N|M|d) {

        if (N > M) {

            int t = N; 

            N = M;

            M = t;

        }

        flag = 0;

        memset(hash, 0, sizeof (hash));

        for (int i = N; i <= M; ++i) {

            hash[i] = 1;

            if (dfs(i, 1)) {

                flag = 1;

                break;

            }

            hash[i] = 0;

        }

        if (!flag) {

            puts("No anti-prime sequence exists.");

        }

    }

    return 0;    

}