1018 Public Bike Management（单源最短+DFS搜索）

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分析：求最短路径。如果最短路径有多个，求能带的最少的自行车数目的那条。如果还是有很多条不同的路，那么就找一个从车站带回的自行车数目最少的

调成了21/30.
还在看哪里写错了，这题写了快1天了,orz。。。
打算换一种方法，在最短路径后，直接dfs，把所有满足最短路情况的路径都存在vecoctor中，然后继续一个sort排序，输出第一个即可。
可以参考这个作者的博客：https://www.cnblogs.com/weedboy/p/7256552.html

得分：21/30

#include<bits/stdc++.h>
#define inf 0x3f3f3f3f
#define maxn 510
using namespace std;
int mp[maxn][maxn],vis[maxn],lowcost[maxn];
int bike[maxn],visit[maxn];
int path[maxn],pre[maxn];
int cmax,n,sp,m,ans,maxBike;
int minNeed=-inf,minBack=inf;
vector<int> tp,pp;
int dijkstra(int s,int e){
    for(int i=0;i<=n;i++){lowcost[i]=mp[s][i];}
    vis[s]=1;
    lowcost[s]=0;
    for(int i=0;i<=n;i++){
        int minn=inf;
        int v=-1;
        for(int j=0;j<=n;j++){
            if(!vis[j]&&lowcost[j]<minn){
                minn=lowcost[j];
                v=j;
            }
        }
        if(v==-1) break;
        vis[v]=1;
        for(int j=0;j<=n;j++){
            if(!vis[j]&&lowcost[v]+mp[v][j]<lowcost[j]){
                lowcost[j]=lowcost[v]+mp[v][j];
            }
        }
    }
    return lowcost[e];
}
void dfs(int x,int dis,int need,int backk){
    visit[x]=1;
    //cout<<"dis= "<<dis<<endl;
    if(dis>ans){return ;}
    if(x==sp &&dis==ans){
        //cout<<need<<" "<<minNeed<<endl;
        if(need>minNeed){
            minNeed=need;
            minBack=backk;
            pp=tp;
        }
        else if(need==minNeed&&backk<minBack){
            minBack=backk;
            pp=tp;
        }
       // cout<<"minNeed= "<<minNeed<<endl;
        return ;
    }
    for(int i=1;i<=n;i++){
        if(!visit[i]&&mp[x][i]!=inf){
           // cout<<"i= "<<i<<endl;
            visit[i]=1;
            tp.push_back(i);
            if(bike[i]>0){
                dfs(i,dis+mp[x][i],need,backk+bike[i]);
            }
            else{
                if(bike[i]<0&&backk>(-1*bike[i])){
                    dfs(i,dis+mp[x][i],need,backk+bike[i]);
                }
                else{
                    dfs(i,dis+mp[x][i],need+(backk+bike[i]),0);
                }
            }
            visit[i]=0;
            tp.pop_back();
        }
    }
    return ;
}

int main(){
    for(int i=0;i<maxn;i++){
        for(int j=0;j<maxn;j++){
            mp[i][j]=inf;
        }
        mp[i][i]=0;
    }
    cin>>cmax>>n>>sp>>m;
    for(int i=1;i<=n;i++){
        cin>>bike[i];
        bike[i]-=cmax/2;
    }
    for(int i=0;i<m;i++){
        int x,y,z;
        cin>>x>>y>>z;
        if(mp[x][y]>z){mp[x][y]=mp[y][x]=z;}
    }
    ans=dijkstra(0,sp);

    dfs(0,0,0,0);
    int tmpp=-1*minNeed;
    if(tmpp<0){
        cout<<"0 0";
    }
    else{
        cout<<-1*minNeed<<" 0";
    }

    for(int i=pp.size()-2;i>=0;i--){
        cout<<"->"<<pp[i];
    }
    cout<<"->"<<sp;
    cout<<" "<<minBack<<endl;
    return 0;
}

#include<bits/stdc++.h>
#define inf 0x3f3f3f3f
#define maxn 510
using namespace std;
int mp[maxn][maxn],vis[maxn],lowcost[maxn];
int bike[maxn],visit[maxn];
int path[maxn],pre[maxn];
int cmax,n,sp,m,ans,maxBike;
int dijkstra(int s,int e){
    for(int i=0;i<=n;i++){lowcost[i]=mp[s][i];}
    vis[s]=1;
    lowcost[s]=0;
    for(int i=0;i<=n;i++){
        int minn=inf;
        int v=-1;
        for(int j=0;j<=n;j++){
            if(!vis[j]&&lowcost[j]<minn){
                minn=lowcost[j];
                v=j;
            }
        }
        if(v==-1) break;
        vis[v]=1;
        for(int j=0;j<=n;j++){
            if(!vis[j]&&lowcost[v]+mp[v][j]<lowcost[j]){
                lowcost[j]=lowcost[v]+mp[v][j];
            }
        }
    }
    return lowcost[e];
}
void dfs(int x,int dis,int bikeNum){
    visit[x]=1;
    if(dis>ans){return ;}
    if(x==sp &&dis==ans){
        if(bikeNum>maxBike){
            //cout<<"bikeNum= "<<bikeNum<<endl;
            maxBike=bikeNum;
            memcpy(path,pre,sizeof(pre));
        }
        return ;
    }
    for(int i=1;i<=n;i++){
        if(!visit[i]&&mp[x][i]!=inf){
            pre[i]=x;
            visit[i]=1;
            dfs(i,dis+mp[x][i],bikeNum+bike[i]-cmax/2);
            visit[i]=0;
        }
    }
}

int main(){
    for(int i=0;i<maxn;i++){
        for(int j=0;j<maxn;j++){
            mp[i][j]=inf;
        }
        mp[i][i]=0;
    }
    cin>>cmax>>n>>sp>>m;
    for(int i=1;i<=n;i++){cin>>bike[i];}
    for(int i=0;i<m;i++){
        int x,y,z;
        cin>>x>>y>>z;
        if(mp[x][y]>z){mp[x][y]=mp[y][x]=z;}
    }
    ans=dijkstra(0,sp);

    maxBike=-inf;
    dfs(0,0,0);
    int b[maxn];
    int curr=0;
    b[curr++]=sp;
    while(1){
        b[curr++]=path[sp];
        if(path[sp]==0) {path[curr]=0;break;}
        sp=path[sp];
    }
    cout<<curr<<" ";
    for(int i=curr-1;i>=0;i--){
        cout<<b[i];
        if(i!=0) {cout<<"->";}
        else {cout<<" ";}
    }
    if(maxBike<=0) {cout<<"0"<<endl;}
    else{
        cout<<maxBike<<endl;
    }
    return 0;
}