POJ2391_Ombrophobic Bovines

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#define maxn 1122
#define maxm 555555
typedef long long ll;
using namespace std;

ll inf=~0U>>2;
ll to[maxm],next[maxm],c[maxm],first[maxn],edge;
ll cow[maxn],hold[maxn],d[maxn],tag[maxn],TAG=520;
ll Q[maxm],bot,top;
ll dis[maxn][maxn],f[maxn],g[maxn][maxn];
bool can[maxn];
ll n,m,sumcow,ans,s,t;

void _init()
{
    sumcow=0;
    for (int i=1; i<=n; i++)
        for (int j=1; j<=n; j++) dis[i][j]=-1;
}

void spfa(ll x)
{
    for (int i=1; i<=n; i++) f[i]=inf;
    Q[bot=top=1]=x,f[x]=0;
    while (bot<=top)
    {
        ll cur=Q[bot++];
        for (int i=1; i<=n; i++)
            if (dis[cur][i]!=-1 && f[cur]+dis[cur][i]<f[i])
            {
                Q[++top]=i;
                f[i]=f[cur]+dis[cur][i];
            }
    }
    for (int i=1; i<=n; i++) g[x][i]=f[i];
}

void _input()
{
    ll U,V,W;
    for (int i=1; i<=n; i++) scanf("%I64d%I64d",&cow[i],&hold[i]),sumcow+=cow[i];
    while (m--)
    {
        scanf("%I64d%I64d%I64d",&U,&V,&W);
        if (dis[U][V]==-1) dis[U][V]=dis[V][U]=W;
            else if (W<dis[U][V]) dis[U][V]=dis[V][U]=W;
    }
    for (int i=1; i<=n; i++) if (cow[i]>0) spfa(i);
}

void addedge(ll U,ll V,ll W)
{
    edge++;
    to[edge]=V,c[edge]=W,next[edge]=first[U],first[U]=edge;
    edge++;
    to[edge]=U,c[edge]=0,next[edge]=first[V],first[V]=edge;
}

bool bfs()
{
    Q[bot=top=1]=t,d[t]=0,tag[t]=++TAG;
    while (bot<=top)
    {
        ll cur=Q[bot++];
        for (int i=first[cur]; i!=-1; i=next[i])
        {
            if (c[i^1]>0 && tag[to[i]]!=TAG)
            {
                tag[to[i]]=TAG,Q[++top]=to[i];
                d[to[i]]=d[cur]+1,can[to[i]]=false;
                if (to[i]==s) return true;
            }
        }
    }
    return false;
}

ll dfs(ll cur,ll num)
{
    if (cur==t) return num;
    ll tmp=num,k;
    for (int i=first[cur]; i!=-1; i=next[i])
        if (c[i]>0 && d[to[i]]==d[cur]-1 && tag[to[i]]==TAG && !can[to[i]])
        {
            k=dfs(to[i],min(c[i],num));
            if (k) num-=k,c[i]-=k,c[i^1]+=k;
            if (num==0) break;
        }
    if (num) can[cur]=true;
    return tmp-num;
}

bool check(ll x)
{
    s=0,t=2*n+1,edge=-1,ans=0;
    for (int i=s; i<=t; i++) first[i]=-1;
    for (int i=1; i<=n; i++)
    {
        if (cow[i]>0)
        {
            addedge(s,i,cow[i]);
            for (int j=1; j<=n; j++)
                if (g[i][j]<=x) addedge(i,j+n,cow[i]);
        }
        addedge(i+n,t,hold[i]);
    }
    while (bfs()) ans+=dfs(s,inf);
    return ans==sumcow;
}

int main()
{
    inf*=inf;
    while (scanf("%I64d%I64d",&n,&m)!=EOF)
    {
        _init();
        _input();
        if (!check(inf-1))
        {
            puts("-1");
            continue;
        }
        ll l=0,r=inf-2,mid;
        while (l<r)
        {
            mid=l/2+r/2;
            if (l&r&1) mid++;
            if (check(mid)) r=mid;
                else l=mid+1;
        }
        printf("%I64d\n",l);
    }
    return 0;
}