P2761 软件补丁问题

P2761 软件补丁问题

思路

貌似不用网络流，直接状态压缩

用spfa跑最短路，直接判断是否能过

位运算太渣了，WA了好几发

代码

#include <bits/stdc++.h>
using namespace std;
const int N = 21, M = 101, inf = 0x3f3f3f3f;
int read() {
    int x = 0, f = 1; char s = getchar();
    for(; s > '9' || s < '0'; s = getchar()) if(s == '-') f = -1;
    for(; s >= '0' && s <= '9'; s = getchar()) x = x * 10 + s - '0';
    return x * f;
}
int n, m, tim[M], dis[1<<N], b1[M], b2[M], f1[M], f2[M];
bool vis[1<<N];
char s[N];
void spfa() {
    memset(dis, 0x3f, sizeof(dis));
    dis[(1<<n)-1] = 0;
    queue<int> q;
    q.push((1<<n)-1);
    while(!q.empty()) {
        int u = q.front();
        q.pop();
        vis[u] = 0;
        for(int i = 1; i <= m; ++i) {
            int v = (u & (~f1[i])) | f2[i];
            if(dis[v] > dis[u] + tim[i]) {
                if((u & b2[i]) == 0 && ((u | b1[i]) == u)) {
                    dis[v] = dis[u] + tim[i];
                    if(!vis[v]) {
                        vis[v] = 1;
                        q.push(v);
                    }
                }
            }
        }
    }
}
int main() {
    n = read(), m = read();
    for(int i = 1; i <= m; ++i) {
        tim[i] = read();
        scanf("%s", s);
        for(int j = 0; j < n; ++j) {
            if(s[j] == '+') b1[i] |= (1<<j);
            else if(s[j] == '-') b2[i] |= (1<<j);
        }
        scanf("%s", s);
        for(int j = 0; j < n; ++j) {
            if(s[j] == '-') f1[i] |= (1<<j);
            else if(s[j] == '+') f2[i] |= (1<<j);
        }
    }
    spfa();
    if(dis[0] == inf) dis[0] = 0;
    printf("%d\n", dis[0]);
    return 0;
}