hdu 2433

考虑删掉每条边会不会影响最短路之和

标记

暴力求解

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>

const int N = 110;

int dis[N], vis[N], Map[N][N], sum[N], used[N][N][N];
int A[N * 30], B[N * 30];
int n, m;
std:: queue <int> Q;

inline int Bfs(int start, int opt) {
    for(int i = 1; i <= n; i ++) vis[i] = 0, dis[i] = 0;
    
    Q.push(start);
    vis[start] = 1;
    while(!Q.empty()) {
        int topp = Q.front();
        Q.pop();
        for(int i = 1; i <= n; i ++) {
            if(!vis[i] && (Map[topp][i] > 0 || Map[i][topp] > 0)) {
                vis[i] = 1;
                if(! opt) used[start][topp][i] = used[start][i][topp] = 1;
                dis[i] += dis[topp] + 1;
                Q.push(i);
            }
        }
    }
    int ret = 0;
    for(int i = 1; i <= n; i ++) {
        if(!dis[i] && i != start) return -1;
        ret += dis[i];
    }
    return ret;
}

int main() {
    while(~ (scanf("%d%d", &n, &m))) {
        memset(Map, 0, sizeof Map);
        memset(used, 0, sizeof used);
        memset(sum, 0, sizeof sum); 
        for(int i = 1; i <= m; i ++) {
            std:: cin >> A[i] >> B[i];
            Map[A[i]][B[i]] ++, Map[B[i]][A[i]] ++;
        }
        int Flag = 0;
        for(int i = 1; i <= n; i ++) {
            sum[i] = Bfs(i, 0);
            if(sum[i] == -1) {
                Flag = -1; break;
            } else Flag += sum[i];
        }
        for(int i = 1; i <= m; i ++) {
            int Nowtot = Flag;
            Map[A[i]][B[i]] --, Map[B[i]][A[i]] --;
            if(Map[A[i]][B[i]] > 0) std:: cout << Nowtot << "\n";
            else if(Nowtot == -1) std:: cout << "INF\n";
            else {
                bool flag = 0;
                for(int j = 1; j <= n; j ++)
                    if(used[j][A[i]][B[i]] == 1) {
                        Nowtot -= sum[j];
                        int tmp = Bfs(j, 1);
                        if(tmp == -1) {flag = 1; break;}
                        Nowtot += tmp;
                    }
                if(flag) std:: cout << "INF\n";
                else std:: cout << Nowtot << "\n";
            }
            Map[A[i]][B[i]] ++, Map[B[i]][A[i]] ++;
        }
    }
    return 0;
}