BZOJ3931 [CQOI2015]网络吞吐量（洛谷P3171）

最短路 最大流

BZOJ题目传送门
洛谷题目传送门

刷一遍最短路，只留下那些最短路的边，然后拆点跑最大流就好了。

代码：

#include
#include
#include
#include
#include
#define N 1005
#define M 100005
#define F inline
using namespace std;
typedef long long LL;
const LL inf=1e18;
struct edg{ int nxt,to; LL d; }e[M<<1];
struct edge{ int nxt,to; LL v,f; }ed[M<<1];
struct P{ int x; LL d; };
int n,m,k,s,t,ti,h[N],h1[N],tmp[N],f[N];
LL d[N],ans;
priority_queue 
 q1; queue <int> q;
F bool operator < (P a,P b){ return a.d>b.d; }
F char readc(){
    static char buf[100000],*l=buf,*r=buf;
    if (l==r) r=(l=buf)+fread(buf,1,100000,stdin);
    return l==r?EOF:*l++;
}
F int _read(){
    int x=0; char ch=readc();
    while (!isdigit(ch)) ch=readc();
    while (isdigit(ch)) x=(x<<3)+(x<<1)+(ch^48),ch=readc();
    return x;
}
#define add(x,y,z) e[++k]=(edg){h1[x],y,z},h1[x]=k
F void addedge(int x,int y,LL z){
    ed[++k]=(edge){h[x],y,z},h[x]=k;
    ed[++k]=(edge){h[y],x,0},h[y]=k;
}
F void Dij(){
    for (int i=1;i<=n;i++) d[i]=inf;
    for (q1.push((P){n,d[n]=0});!q1.empty();q1.pop()){
        if (q1.top().d>d[q1.top().x]) continue; int x;
        for (int i=h1[x=q1.top().x],v;i;i=e[i].nxt)
            if (d[x]+e[i].dfor (int x=1;x<=n;x++)
        for (int i=h1[x],v;i;i=e[i].nxt)
            if (e[i].d+d[x]==d[v=e[i].to])
                addedge(v+n,x,inf);
}
F bool bfs(){
    while (!q.empty()) q.pop();
    d[s]=0,f[s]=++ti,q.push(s);
    while (!q.empty()){
        int x=q.front(); q.pop();
        for (int i=h[x],v;i;i=ed[i].nxt)
            if (ed[i].v>ed[i].f&&f[v=ed[i].to]!=ti)
                d[v]=d[x]+1,f[v]=ti,q.push(v);
    }
    return f[t]==ti;
}
LL dfs(int x,LL rem){
    if (x==t||!rem) return rem; LL sum=0;
    for (int &i=tmp[x];i;i=ed[i].nxt)
        if (d[ed[i].to]==d[x]+1){
            LL p=dfs(ed[i].to,min(rem,ed[i].v-ed[i].f));
            if (p) sum+=p,ed[i].f+=p,ed[i^1].f-=p,rem-=p;
            if (!rem) break;
        }
    return sum;
}
int main(){
    n=_read(),m=_read(),s=1,t=n<<1;
    for (int i=1,x,y,z;i<=m;i++)
        x=_read(),y=_read(),z=_read(),add(x,y,z),add(y,x,z);
    k=1,Dij();
    for (int i=1,x;i<=n;i++)
        x=_read(),addedge(i,i+n,(i!=1&&i!=n)?x:inf);
    while (bfs()) memcpy(tmp,h,sizeof(h)),ans+=dfs(s,inf);
    return printf("%lld\n",ans),0;
}