BZOJ4500矩陣 差分約束判解

我們首先建圖，然後對其進行SPFA差分約束判斷負權迴路，注意開始將點全放入隊列。

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<queue>
#include<vector>
#include<climits>
#include<string>
#include<cstdlib>
#include<set>
#include<stack>
#include<map>
#include<bitset>
#include<ctime>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
inline ll read()
{
    char k=0;char ls;ls=getchar();for(;ls<'0'||ls>'9';k=ls,ls=getchar());
    ll x=0;for(;ls>='0'&&ls<='9';ls=getchar())x=x*10+ls-'0';
    if(k=='-')x=0-x;return x;
}

ll n,m,k,t;
struct E
{
    ll edge;
    ll zhi;
    ll s;
}e[100000];
ll last[10000];
ll w;
ll dis[10000];
ll vis[10000];
ll ti[10000];
ll pan[10000];
ll spfa()
{
    queue<ll>q;
    for(int i=1;i<=n+m;++i)
    {
        q.push(i);
        pan[i]=1;   
    }
    memset(dis,0,sizeof(dis));
    memset(vis,0,sizeof(vis));
    memset(ti,0,sizeof(ti));
    while(!q.empty())
    {
        ll x=q.front();q.pop();pan[x]=0;
        for(ll j=last[x];j;j=e[j].zhi)
        {
            ll d=e[j].edge;
            if(dis[d]>dis[x]+e[j].s)
            {
                dis[d]=dis[x]+e[j].s;
                if(pan[d]==0)
                {
                    pan[d]=1;
                    q.push(d);
                    ++ti[d];
                    if(ti[d]>n+m)return 0;
                }               
            }
        }
    }
    return 1;
}



int main()
{
    //freopen("matrix.in","r",stdin);
    //freopen("matrix.out","w",stdout);
    t=read();
    while(t--)
    {
        n=read(),m=read(),k=read();
        memset(last,0,sizeof(last));
        w=0;
        for(int i=1;i<=k;++i)
        {
            ll a1=read(),b1=read(),c1=read();
            e[++w].edge=a1;
            e[w].s=c1;
            e[w].zhi=last[n+b1];
            last[n+b1]=w;

            e[++w].edge=n+b1;
            e[w].s=-c1;
            e[w].zhi=last[a1];
            last[a1]=w;
        }
        if(spfa())cout<<"Yes"<<endl;
        else cout<<"No"<<endl;
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}