洛谷P2761 软件补丁问题(状压DP,SPFA)

题意

描述不清。。。

Sol

网络流24题里面怎么会有状压dp？？

真是狗血，不过还是简单吧。

直接用$f[sta]$表示当前状态为$sta$时的最小花费

转移的时候枚举一下哪一个补丁可以搞这个状态

但是这玩意儿有后效性，可以用SPFA消去

 

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int MAXN = 101, INF = 1e9 + 10;
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = 1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int N, M;
int tim[MAXN], dis[2097153], B1[MAXN], B2[MAXN], F1[MAXN], F2[MAXN], vis[2097153];
int SPFA() {
    queue<int> q; 
    q.push((1 << N) - 1); dis[(1 << N) - 1] = 0;
    while(!q.empty()) {
        int sta = q.front(); q.pop(); vis[sta] = 0;
        for(int i = 1; i <= M; i++) {
            int now = sta;
            if(((sta & B1[i]) == B1[i]) && ((sta & B2[i]) == 0)) {
                now = now & (~F1[i]);
                now = now | F2[i];
                if(dis[now] > dis[sta] + tim[i]) {
                    dis[now] = dis[sta] + tim[i];
                    if(!vis[now]) q.push(now);
                }
            }
        }
    }
    return dis[0] < INF ? dis[0] : 0;
}
int main() {
    N = read(); M = read();
    memset(dis, 0x3f, sizeof(dis));
    for(int i = 1; i <= M; i++) {
        char s1[21], s2[21];
        scanf("%d %s %s", &tim[i], s1, s2);
        for(int j = 0; j < N; j++)
            if(s1[j] == '+') B1[i] |= 1 << j;
            else if(s1[j] == '-') B2[i] |= 1 << j;
        for(int j = 0; j < N; j++)
            if(s2[j] == '-') F1[i] |= 1 << j;
            else if(s2[j] == '+') F2[i] |= 1 << j;
    }
    printf("%d", SPFA());
    return 0;
}
/*
3 3
1 000 00-
1 00- 0-+
2 0-- -++

*/