FOJ 254. Worm Squares

Algorithm

競程作業，以前交大年度賽的題目：FOJ-254

Flow network，把源點指向所有的 H，然後 H 指向 B，B 指向 T，T 指向匯點
然後跑 Edmonds–Karp

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# include <bits/stdc++.h>
using namespace std;

# define ll long long
# define ui unsigned int
# define ull unsigned long long
# define INF 1023456789
# define jizz cin.tie(0);ios_base::sync_with_stdio(0);

void solve(){
    int n, m, t, s=0;
    char tmpc;
    cin>>n>>m;
    t = n*m+1;
    vector<vector<int>> M(n+1, vector<int>(m+1));
    vector<vector<int>> adj(n*m+4, vector<int>(n*m+4, 0));
    for(int i=0; i<n; i++){
        for(int j=1; j<=m; j++){
            cin>>tmpc;
            if(tmpc=='H') M[i][j] = 0;
            else if(tmpc=='B') M[i][j] = 1;
            else M[i][j] = 2;
            if(i>0){
                if(M[i-1][j]==M[i][j]+1){
                    adj[i*m+j][(i-1)*m+j] = 1;
                }
                if(M[i-1][j]==M[i][j]-1){
                    adj[(i-1)*m+j][i*m+j] = 1;
                }
            }
            if(j>1){
                if(M[i][j-1]==M[i][j]+1){
                    adj[i*m+j][i*m+j-1] = 1;
                }
                if(M[i][j-1]==M[i][j]-1){
                    adj[i*m+j-1][i*m+j] = 1;
                }
            }
            if(M[i][j]==0){
                adj[s][i*m+j] = 1;
            }
            if(M[i][j]==2){
                adj[i*m+j][t] = 1;
            }
        }
    }
    int now, l, ans=0, dot, f;
    while(1){
        int i;
        queue<int> Q;
        vector<bool> visited(n*m+4, 0);
        vector<int> bt(n*m+4);
        bt[s] = -1;
        Q.push(s);
        while(!Q.empty()){
            now = Q.front();
            Q.pop();
            for(i=1; i<=n*m+1; i++){
                if(adj[now][i]&&!visited[i]){
                    bt[i] = now;
                    visited[i] = 1;
                    if(i==t) break;
                    Q.push(i);
                }
            }
            if(i==t) break;
        }
        if(i!=t){
            for(int j=1; j<=n*m; j++){
                if(adj[t][j]) ans++;
            }
            cout<<ans<<"\n";
            return ;
        }
        dot = t;
        while(dot!=s){
            adj[dot][bt[dot]]++;
            adj[bt[dot]][dot]--;
            dot = bt[dot];
        }
    }
}

int main(){jizz
    int t;
    cin>>t;
    while(t--){
        solve();
    }
}