#include<iostream>
#include<string>
#include<cstring>
#include<sstream>
#include<vector>
#include<algorithm>
#include<queue>
#include<cstdio>
using namespace std;
const int maxn=3000+10;
const int INF=100000000;
struct Edge{
int from,to,dist;
Edge(int u,int v,int d):from(u),to(v),dist(d){}
};
struct BellmanFord{
int n,m;
vector<Edge>edges;
vector<int>G[maxn];
int p[maxn];
int d[maxn];
int inq[maxn];
int cnt[maxn];
void init(int n){
this->n=n;
edges.clear();
for(int i=0;i<n;i++)G[i].clear();
}
void AddEdge(int from,int to,int dist){
edges.push_back(Edge(from,to,dist));
m=edges.size();
G[from].push_back(m-1);
}
bool negativeCycle(){
queue<int>q;
memset(inq,0,sizeof(inq));
memset(cnt,0,sizeof(cnt));
for(int i=0;i<n;i++){d[i]=0;q.push(i);}
while(!q.empty()){
int u=q.front();q.pop();
inq[u]=0;
for(int i=0;i<G[u].size();i++){
Edge& e=edges[G[u][i]];
if(d[e.to]>d[u]+e.dist){
d[e.to]=d[u]+e.dist;
p[e.to]=G[u][i];
if(!inq[e.to]){
q.push(e.to);inq[e.to]=1;
if(++cnt[e.to]>n)return false;
}
}
}
}
return true;
}
};
BellmanFord solver;
bool test(int x)
{
for(int i=0;i<solver.m;i++)
solver.edges[i].dist-=x;
bool ret=solver.negativeCycle();
for(int i=0;i<solver.m;i++)
solver.edges[i].dist+=x;
return ret;
}
int n,m;
int main()
{
while(scanf("%d%d",&n,&m)==2){
solver.init(n);
int u,v,d;
int ud=0;
for(int i=0;i<m;i++){
scanf("%d%d%d",&u,&v,&d);ud=max(ud,d);
u--;v--;
solver.AddEdge(u,v,d);
}
if(test(ud+1))printf("Infinite\n"); // 如果可以让每条边权都>ub,说明每条边的权都增加了,重复一次会增加得更多...直到无限
else if(!test(1))printf("No Solution\n");
else{
int L=2,R=ud,ans=1;
while(L<=R){
int mid=(L+R)/2;
if(test(mid)){ans=mid;L=mid+1;}
else R=mid-1;
}
printf("%d\n",ans);
}
}
return 0;
}
UVa11478 - Halum
最新推荐文章于 2018-01-23 19:32:00 发布