BZOJ1305/Luogu3153 [CQOI2009]dance跳舞 (network flow)

#define T 1001
#define S 0

struct Edge{
	int nxt,pre,w;
}e[500007];
int cntEdge,head[N];
inline void add(int u,int v,int w){
	e[++cntEdge] = (Edge){head[u], v, w}, head[u] = cntEdge;
}

inline void Add(int u,int v,int w){
	add(u, v, w);
	add(v, u, 0);
}

int q[N],h[N];
inline bool BFS(){
	int t = 0, w = 1;
	Fill(h, -1);
	h[0] = 0, q[0] = 0;
	while(t != w){
		int u = q[t++];
		for(register int i = head[u]; i; i =e[i].nxt){
			int v = e[i].pre;
			if(e[i].w && h[v] == -1){
				h[v] = h[u] + 1;
				q[w++] = e[i].pre;
			}
		}
	}
	return h[T] != -1;
}
inline int DFS(int u, int f){
	if(u == T) return f;
	int w, used = 0;
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(h[v] == h[u] + 1){
			w = DFS(v, Min(f - used, e[i].w));
			e[i].w -= w, e[i^1].w += w;
			used += w;
			if(used == f) return f;
		}
	}
	if(!used) h[u] = -1;
	return used;
}
inline int Dinic(){
	int sum = 0;
	while(BFS()){
		sum += DFS(0, 0x7fffffff);
	}
	return sum;
}

int n,k,mp[N][N];

inline void Build(int &mid){
    cntEdge=1;
	Fill(head, 0);

	R(i,1,n) Add(S, i, mid);
	R(i,1,n) Add(i, i + 500, k);
	R(i,1,n) Add(i + n + 500, i + n, k);
    R(i,1,n) Add(i + n, T, mid);
    R(i,1,n){
    	R(j,1,n){
    		if(mp[i][j])
    			Add(i, n + j, 1);
    		else
    			Add(i + 500, n + j + 500, 1);
    	}
	}
}

int main(){
    io >> n >> k;
    R(i,1,n){
    	char str[57];
    	scanf("%s", str + 1);
    	R(j,1,n)
    		mp[i][j] = (str[j] == 'Y');
    }

    int maxx = 0;
	int l = 0, r = 50;
    while(l<=r){
        int mid = (l + r) >> 1;
        Build(mid);
		int ans = Dinic();
        if(ans >= n * mid){
			maxx = mid;
			l = mid + 1;
		}
        else
			r = mid - 1;
    }

    printf("%d", maxx);
    return 0;
}