这道题目很奇怪.
为什么奇怪?因为这道题用了一种叫分治最小割/最小割树的玩意.
以前从来没有见过这东西.
推荐一个讲这玩意的博客
写起来还是很顺手的.
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<string>
#include<iomanip>
#include<algorithm>
#include<map>
using namespace std;
#define ll long long
#define FILE "dealing"
#define up(i,j,n) for(int i=j;i<=n;++i)
#define db double
#define uint unsigned ll
#define eps 1e-12
#define pii pair<ll,ll>
ll read(){
ll x=0,f=1,ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
return f*x;
}
const ll maxn=20500,limit=1e6,mod=(ll)(7+1e9+0.1);
const ll inf=(ll)(1e9);
template<class T>bool cmax(T& a,T b){return a<b?a=b,true:false;}
template<class T>bool cmin(T& a,T b){return a>b?a=b,true:false;}
template<class T>T min(T& a,T& b){return a<b?a:b;}
template<class T>T max(T& a,T& b){return a>b?a:b;}
int n,m,S,T,id[maxn],vis[maxn],tmp[maxn],w[maxn],tot=0;
struct node{
int y,next,flow,rev;
}e[maxn];
int len=1,linkk[maxn];
void insert(int x,int y,int flow){
e[++len].y=y;
e[len].next=linkk[x];
linkk[x]=len;
e[len].flow=flow;
e[len].rev=len+1;
e[++len].y=x;
e[len].next=linkk[y];
linkk[y]=len;
e[len].flow=flow;
e[len].rev=len-1;
}
int d[maxn],q[maxn],head,tail;
bool makelevel(){
up(i,1,n)d[i]=-1;
d[S]=0;head=tail=0;
q[++tail]=S;
while(++head<=tail){
int x=q[head];
for(int i=linkk[x];i;i=e[i].next)
if(d[e[i].y]==-1&&e[i].flow)d[e[i].y]=d[x]+1,q[++tail]=e[i].y;
}
return d[T]!=-1;
}
int makeflow(int x,int flow){
if(x==T||!flow)return flow;
int maxflow=0,dis=0;
for(int i=linkk[x];i&&maxflow<flow;i=e[i].next){
if(d[e[i].y]==d[x]+1&&e[i].flow)
if(dis=makeflow(e[i].y,min(flow-maxflow,e[i].flow))){
e[i].flow-=dis;
e[i^1].flow+=dis;
maxflow+=dis;
}
}
if(!maxflow)d[x]=-1;
return maxflow;
}
int dinic(){
int ans=0,d;
while(makelevel())
while(d=makeflow(S,inf))
ans+=d;
return ans;
}
void dfs(int x){
vis[x]=1;
for(int i=linkk[x];i;i=e[i].next){
if(e[i].flow&&!vis[e[i].y])
dfs(e[i].y);
}
}
void divide(int l,int r){
if(l==r)return;
for(int i=2;i<=len;i+=2)
e[i].flow=e[i^1].flow=(e[i].flow+e[i^1].flow)>>1;
S=id[l],T=id[r];
int maxflow=dinic();
w[++tot]=maxflow;
up(i,1,n)vis[i]=0;
dfs(S);
int L=l,R=r;
up(i,l,r){
if(vis[id[i]])tmp[L++]=id[i];
else tmp[R--]=id[i];
}
up(i,l,r)id[i]=tmp[i];
divide(l,L-1);divide(R+1,r);
}
int main(){
freopen(FILE".in","r",stdin);
freopen(FILE".out","w",stdout);
n=read(),m=read();
up(i,1,n)id[i]=i;
up(i,1,m){
int x=read(),y=read(),v=read();
insert(x,y,v);
}
divide(1,n);
sort(w+1,w+tot+1);
w[0]=-1;
int ans=0;
up(i,1,tot)if(w[i]!=w[i-1])ans++;
printf("%d
",ans);
return 0;
}