最短路

Floyed

http://codevs.cn/problem/1077/

#include<cstdio>
const int N=105;
typedef long long ll; 
ll dis[N][N];
int main(){
    int n,q;
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
        for(int j=1;j<=n;++j) scanf("%lld",&dis[i][j]);
    for(int k=1;k<=n;++k)
        for(int i=1;i<=n;++i)
            for(int j=1;j<=n;++j)
                if(dis[i][k]+dis[k][j]<dis[i][j]) dis[i][j]=dis[i][k]+dis[k][j];
    scanf("%d",&q);
    for(int i=1;i<=q;++i){
        int u,v;
        scanf("%d%d",&u,&v);
        printf("%lld\n",dis[u][v]);
    }
    return 0;
}

 利用floyed求最小环

http://acm.hdu.edu.cn/showproblem.php?pid=1599

无向图

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=105,inf=1061109567;
int dis[N][N],lb[N][N];
int main(){
    int n,m,u,v,w;
    while(scanf("%d%d",&n,&m)!=EOF){
        int ans=inf;
        memset(dis,0x3f,sizeof(dis));
        memset(lb,0x3f,sizeof(lb));
        while(m--){
            scanf("%d%d%d",&u,&v,&w);
            lb[u][v]=lb[v][u]=dis[u][v]=dis[v][u]=min(lb[u][v],w);
        }
        for(int k=1;k<=n;++k){
            for(int i=1;i<k;++i)
                if(lb[i][k]<inf)
                    for(int j=i+1;j<k;++j)
                        if(lb[j][k]<inf) ans=min(ans,lb[i][k]+lb[k][j]+dis[i][j]);
            for(int i=1;i<=n;++i)
                for(int j=1;j<=n;++j)
                    if(lb[i][k]>0) dis[i][j]=min(dis[i][j],dis[i][k]+dis[k][j]);     
        }
        if(ans==inf) printf("It's impossible.\n");
        else printf("%d\n",ans);
    }
    return 0;
}

lg4779

 https://www.luogu.org/problemnew/show/P4779

dijkstra

#include<cstdio>
#include<queue>
#include<cstring> 
using namespace std;
const int N=1e5+5;
struct E{
    int v,n,q;
}e[N*5];
int fir[N],s,dis[N],ss;
bool vis[N];
struct F{
    int v,q;
    bool operator<(const F &a)const{
        return q>a.q;
    } 
}st;
priority_queue<F>dl;
void add(int u,int v,int q){
    e[++s].v=v;
    e[s].q=q;
    e[s].n=fir[u];
    fir[u]=s;
}
int main(){
    int n,m,u,v,q;
    scanf("%d%d%d",&n,&m,&st.v);
    while(m--){
        scanf("%d%d%d",&u,&v,&q);
        add(u,v,q);
    }
    dl.push(st);
    for(int i=1;i<=n;++i) dis[i]=2147483647;
    dis[st.v]=0;
    while(!dl.empty()){
        F t=dl.top();dl.pop();
        if(vis[t.v]) continue;
        vis[t.v]=1;++ss;
        for(int i=fir[t.v];i;i=e[i].n)
            if(t.q+e[i].q<dis[e[i].v]){
                dis[e[i].v]=e[i].q+t.q;
                if(!vis[e[i].v]) dl.push((F){e[i].v,dis[e[i].v]});
            }
    }
    for(int i=1;i<=n;++i)
        printf("%d ",dis[i]);
    return 0;
} 

 lg3371

https://www.luogu.org/problemnew/show/P3371

spfa

#include<cstdio>
#include<queue>
using namespace std;
const int N=1e4+5,M=5e5+5;
struct E{
    int v,q,n;
}e[M];
int fir[N],s,dis[N];
queue<int>dl;
bool vis[N];
void add(int u,int v,int q){
    e[++s].v=v;
    e[s].q=q;
    e[s].n=fir[u];
    fir[u]=s;
}
int main(){
    int n,m,st,u,v,q;
    scanf("%d%d%d",&n,&m,&st);
    while(m--){
        scanf("%d%d%d",&u,&v,&q);
        add(u,v,q);
    }
    dl.push(st);
    vis[st]=1;
    for(int i=1;i<=n;++i) dis[i]=2147483647;
    dis[st]=0;
    while(!dl.empty()){
        u=dl.front();dl.pop();
        for(int i=fir[u];i;i=e[i].n)
            if(dis[u]+e[i].q<dis[e[i].v]){
                dis[e[i].v]=dis[u]+e[i].q;
                if(!vis[e[i].v]){
                    vis[e[i].v]=1;
                    dl.push(e[i].v);
                }
            }
        vis[u]=0;
    }
    for(int i=1;i<=n;++i) printf("%d ",dis[i]);
    return 0;
}