【BZOJ-4519】不同的最小割 最小割树（分治+最小割）

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}
#define maxn 1000
#define maxm 100010
int n,m,q,t,ans[maxn],tot,id[maxn],tmp[maxn];
struct Edgenode{int next,to,cap;}edge[maxm];
int head[maxn],cnt=1;
void add(int u,int v,int w)
{cnt++; edge[cnt].to=v; edge[cnt].next=head[u]; head[u]=cnt; edge[cnt].cap=w;}
void insert(int u,int v,int w) {add(u,v,w); add(v,u,w);}
int dis[maxn],que[maxn<<1],cur[maxn],S,T;
bool bfs()
{
    memset(dis,-1,sizeof(dis));
    que[0]=S; dis[S]=0; int he=0,ta=1;
    while (he<ta)
        {
            int now=que[he++];
            for (int i=head[now]; i; i=edge[i].next)
                if (edge[i].cap && dis[edge[i].to]==-1)
                    dis[edge[i].to]=dis[now]+1,que[ta++]=edge[i].to;
        }
    return dis[T]!=-1;
}
int dfs(int loc,int low)
{
    if (loc==T) return low;
    int w,used=0;
    for (int i=cur[loc]; i; i=edge[i].next)
        if (edge[i].cap && dis[edge[i].to]==dis[loc]+1)
            {
                w=dfs(edge[i].to,min(low-used,edge[i].cap));
                edge[i].cap-=w; edge[i^1].cap+=w;
                used+=w; if (edge[i].cap) cur[loc]=i;
                if (used==low) return low;
            }
    if (!used) dis[loc]=-1;
    return used;
}
#define inf 0x7fffffff
int dinic()
{
    int tmp=0;
    while (bfs())
        {
            for (int i=1; i<=n; i++) cur[i]=head[i];
            tmp+=dfs(S,inf);
        }
    return tmp;
}
void init()
{
    cnt=1;
    memset(ans,0,sizeof(ans));
    memset(head,0,sizeof(head));
}
bool visit[maxn];
void DFS(int x)
{
    visit[x]=1;
    for (int i=head[x]; i; i=edge[i].next)
        if (edge[i].cap && !visit[edge[i].to])
            DFS(edge[i].to);
}
void work(int L,int R)
{
    if (L==R) return;
    for (int i=2; i<=cnt; i+=2) 
        edge[i].cap=edge[i^1].cap=(edge[i].cap+edge[i^1].cap)>>1;
    S=id[L],T=id[R];
    int maxflow=dinic();
    memset(visit,0,sizeof(visit)); DFS(S);
    ans[++tot]=maxflow;
    int l=L,r=R;
    for (int i=L; i<=R; i++)
        if (visit[id[i]])
            tmp[l++]=id[i];
        else tmp[r--]=id[i];
    for (int i=L; i<=R; i++) id[i]=tmp[i];
    work(L,l-1); work(r+1,R);
}        
int main()
{
    init();
    n=read(),m=read();
    for (int i=1; i<=n; i++) id[i]=i;
    for (int u,v,w,i=1; i<=m; i++)
    u=read(),v=read(),w=read(),insert(u,v,w);
    work(1,n);
    sort(ans+1,ans+tot+1);
    int an=1;
    for (int i=2; i<=tot; i++) if (ans[i]!=ans[i-1]) an++;
    printf("%d\n",an);
    return 0;
}