poj 3259 Wormholes【Bellman-Ford Vs SPFA】

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http://poj.org/problem?id=3259

用Bellman-Ford和SPFA均可以判负环。。。

SPFA

【856KB 125ms】

#include<iostream>#include<vector>#include<map>#include<stack>#include<algorithm>#include<queue>#include<list>#include<set>#include<string.h>#include<stdlib.h>#include<math.h>#include<stdio.h>#include<ctype.h>#include<iomanip>using namespace std;#define LL long long#define pi acos(-1)#define N 5000#define INF 999999999int n,m,w;int d[N];int cnt[N];int vis[N];struct node{    int to,time;};vector<node> v[N];void init(){    int i,j,k;    int a,b,c;    scanf("%d%d%d",&n,&m,&w);    node p;    for(i=1;i<=n;i++)    {        v[i].clear();        cnt[i]=0;        vis[i]=0;        d[i]=INF;    }    for(i=0;i<m;i++)//双向    {        scanf("%d%d%d",&a,&b,&c);        p.to=b,p.time=c;        v[a].push_back(p);        p.to=a,p.time=c;        v[b].push_back(p);    }    for(i=0;i<w;i++)//单向    {        scanf("%d%d%d",&a,&b,&c);        p.to=b,p.time=-c;        v[a].push_back(p);    }}bool spfa(){    int i,j,k;    queue<int> q;    while(!q.empty())q.pop();    q.push(1);    d[1]=0;    cnt[1]=1;    vis[1]=1;    while(!q.empty())    {        int top=q.front();        q.pop();        vis[top]=0;        for(i=0;i<(int)v[top].size();i++)        {            int to=v[top][i].to;            if(d[to]>d[top]+v[top][i].time)            {                d[to]=d[top]+v[top][i].time;                if(!vis[to])                {                    vis[to]=1;                    cnt[to]++;                    if(cnt[to]>=n)                        return 1;                    q.push(to);                }            }        }    }    return 0;}int main(){ //   freopen("a.txt","r",stdin);    int t;    int i,j,k;    while(scanf("%d",&t)!=EOF)    {        while(t--)        {            init();            if(spfa())            printf("YES\n");            else            printf("NO\n");        }    }    return 0;}

Bellman-Ford 【736KB 125ms】

#include<iostream>#include<vector>#include<map>#include<stack>#include<algorithm>#include<queue>#include<list>#include<set>#include<string.h>#include<stdlib.h>#include<math.h>#include<stdio.h>#include<ctype.h>#include<iomanip>using namespace std;#define LL long long#define pi acos(-1)#define N 5000#define INF 999999999int n,m,w;int cnt;int d[N];struct node{    int a,b,time;}e[N];bool fuck(){    int i,j,k;    for(i=1;i<=n;i++)        d[i]=INF;    d[1]=0;    for(i=1;i<n;i++)    {        for(j=1;j<=cnt;j++)        if(d[e[j].b]>d[e[j].a]+e[j].time)            d[e[j].b]=d[e[j].a]+e[j].time;    }    for(j=1;j<=cnt;j++)       if(d[e[j].b]>d[e[j].a]+e[j].time)       return 1;    return 0;}void init(){    int i,j,k;    cnt=0;    int a,b,c;    scanf("%d%d%d",&n,&m,&w);    for(i=0;i<m;i++)//双向    {        scanf("%d%d%d",&a,&b,&c);        cnt++;        e[cnt].a=a;        e[cnt].b=b;        e[cnt].time=c;        cnt++;        e[cnt].b=a;        e[cnt].a=b;        e[cnt].time=c;    }    for(i=0;i<w;i++)//单向    {        scanf("%d%d%d",&a,&b,&c);        cnt++;        e[cnt].a=a;        e[cnt].b=b;        e[cnt].time=c*(-1);    }}int main(){  //  freopen("a.txt","r",stdin);    int t;    int i,j,k;    while(scanf("%d",&t)!=EOF)    {        while(t--)        {            init();            if(fuck())            printf("YES\n");            else            printf("NO\n");        }    }    return 0;}