PAT A1018

A 1018 Public Bike Management

　　这个题目算是比较典型的一个。我分别用dfs，及dijkstra+dfs实现了一下。

dfs实现代码：

 #include <cstdio>
 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 using namespace std;
 #define MAXNUM 510
 #define CLR(a,b) memset(a,b,sizeof(a));
 const int INF = 0x7f7f7f7f;
 int C, N, Sp, M, dstDis = INF, tmpDstDis = , dstSendBikeNum = INF, dstBackBikeNum = INF;
 vector<int> dstPathVec, tmpPathVec, routeVec[MAXNUM];
 vector<int> bikeNumStaVec(MAXNUM,);
 vector<int> visitFlagVec(MAXNUM,false);
 int route[MAXNUM][MAXNUM];
 void dfs(int u)
 {
     if(u == Sp && tmpDstDis <= dstDis)
     {
         int halfC = C/, tmpBikeNum = , tmpSendBikeNum = , tmpBackBikeNum = ;
         for(int i = ; i < tmpPathVec.size(); ++ i)
         {
             tmpBikeNum += halfC-bikeNumStaVec[tmpPathVec[i]];
             if(tmpBikeNum > )
             {
                 tmpSendBikeNum += tmpBikeNum;
                 tmpBikeNum = ;
             }
         }
         tmpBackBikeNum = -tmpBikeNum;
         if(tmpDstDis < dstDis)
         {
             dstSendBikeNum = tmpSendBikeNum;
             dstBackBikeNum = tmpBackBikeNum;
             dstDis = tmpDstDis;
             dstPathVec = tmpPathVec;
         }
         else if((tmpSendBikeNum < dstSendBikeNum) || (dstSendBikeNum == tmpSendBikeNum && dstBackBikeNum > tmpBackBikeNum))
         {
             dstSendBikeNum = tmpSendBikeNum;
             dstBackBikeNum = tmpBackBikeNum;
             dstDis = tmpDstDis;
             dstPathVec = tmpPathVec;
         }
         return;
     }
     if(tmpDstDis > dstDis)
         return;
     for(auto it = routeVec[u].begin(); it != routeVec[u].end(); ++ it)
     {
         if(!visitFlagVec[*it])
         {
             visitFlagVec[*it] = true;
             tmpPathVec.push_back(*it);
             tmpDstDis += route[u][*it];
             dfs(*it);
             tmpDstDis -= route[u][*it];
             tmpPathVec.pop_back();
             visitFlagVec[*it] = false;
         }
     }
 }
 int main()
 {
     cin >> C >> N >> Sp >> M;
     int tmpSt, tmpEnd, tmpDis;
     for(int i = ; i <= N; ++i)
         cin >> bikeNumStaVec[i];
     CLR(route,0x7f);
     while(M--)
     {
         cin >> tmpSt >> tmpEnd >> tmpDis;
         route[tmpSt][tmpEnd] = tmpDis;
         route[tmpEnd][tmpSt] = tmpDis;
         routeVec[tmpSt].push_back(tmpEnd);
         routeVec[tmpEnd].push_back(tmpSt);
     }
     visitFlagVec[] = true;
     tmpPathVec.push_back();
     dfs();
     cout << dstSendBikeNum;
     for(int i = ; i < dstPathVec.size(); ++i)
     {
         if(i == )  printf(" ");
         else        printf("->");
         cout << dstPathVec[i];
     }
     cout << " " << dstBackBikeNum;
     return ;
 }

dijkstra和dfs实现代码

 #include <cstdio>
 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 using namespace std;
 #define MAXNUM 510
 #define CLR(a,b) memset(a,b,sizeof(a));
 const int INF = 0x7f7f7f7f;
 int C, N, Sp, M, dstSendBikeNum = INF, dstBackBikeNum = INF;
 vector<int> dstPathVec, tmpPathVec, preRoute[MAXNUM];
 vector<int> bikeNumStaVec(MAXNUM,);
 vector<int> visitFlagVec(MAXNUM,false);
 int dis[MAXNUM];
 int route[MAXNUM][MAXNUM];
 void dijkstra(int u)
 {
     dis[u] = ;
     for(int i = ; i <= N; ++ i)
     {
         int tmpMinDis = INF, v = -;
         for(int j = ; j <= N; ++ j)
         {
             if(!visitFlagVec[j] && dis[j] < tmpMinDis)
             {
                 v = j;
                 tmpMinDis = dis[j];
             }
         }
         if(v == - || v == Sp)
             return;
         visitFlagVec[v] = true;
         for(int j = ; j <= N; ++ j)
         {
             if(!visitFlagVec[j] && dis[j] > dis[v] + route[v][j])
             {
                 dis[j] = dis[v] + route[v][j];
                 preRoute[j].clear();
                 preRoute[j].push_back(v);
             }
             else if(!visitFlagVec[j] && dis[j] == dis[v] + route[v][j])
                 preRoute[j].push_back(v);
         }
     }
 }
 void dfs(int u)
 {
     if(u == )
     {
         tmpPathVec.push_back(u);
         int halfC = C/, tmpBikeNum = , tmpSendBikeNum = , tmpBackBikeNum = ;
         for(int i = tmpPathVec.size()-; i >= ; -- i)
         {
             tmpBikeNum += halfC-bikeNumStaVec[tmpPathVec[i]];
             if(tmpBikeNum > )
             {
                 tmpSendBikeNum += tmpBikeNum;
                 tmpBikeNum = ;
             }
         }
         tmpBackBikeNum = -tmpBikeNum;
         if((tmpSendBikeNum < dstSendBikeNum) || (dstSendBikeNum == tmpSendBikeNum && dstBackBikeNum > tmpBackBikeNum))
         {
             dstSendBikeNum = tmpSendBikeNum;
             dstBackBikeNum = tmpBackBikeNum;
             dstPathVec = tmpPathVec;
         }
         tmpPathVec.pop_back();
         return;
     }
     tmpPathVec.push_back(u);
     for(auto it = preRoute[u].begin(); it != preRoute[u].end(); ++ it)
         dfs(*it);
     tmpPathVec.pop_back();
 }
 int main()
 {
     cin >> C >> N >> Sp >> M;
     int tmpSt, tmpEnd, tmpDis;
     for(int i = ; i <= N; ++i)
         cin >> bikeNumStaVec[i];
     CLR(route,0x7f);
     CLR(dis,0x7f);
     while(M--)
     {
         cin >> tmpSt >> tmpEnd >> tmpDis;
         route[tmpSt][tmpEnd] = tmpDis;
         route[tmpEnd][tmpSt] = tmpDis;
     }
     dijkstra();
     dfs(Sp);
     cout << dstSendBikeNum;
     reverse(dstPathVec.begin(), dstPathVec.end());
     for(int i = ; i < dstPathVec.size(); ++i)
     {
         if(i == )  printf(" ");
         else        printf("->");
         cout << dstPathVec[i];
     }
     cout << " " << dstBackBikeNum;
     return ;
 }

另：一种错误(dfs中，最后判断第二条件时出现了错误)

 #include <cstdio>
 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 using namespace std;
 #define MAXNUM 510
 #define CLR(a,b) memset(a,b,sizeof(a));
 const int INF = 0x7f7f7f7f;
 int C, N, Sp, M, dstSendBikeNum = INF, dstBackBikeNum = INF;
 vector<int> dstPathVec, tmpPathVec, preRoute[MAXNUM];
 vector<int> bikeNumStaVec(MAXNUM,);
 vector<int> visitFlagVec(MAXNUM,false);
 int dis[MAXNUM];
 int route[MAXNUM][MAXNUM];
 void dijkstra(int u)
 {
     dis[u] = ;
     for(int i = ; i <= N; ++ i)
     {
         int tmpMinDis = INF, v = -;
         for(int j = ; j <= N; ++ j)
         {
             if(!visitFlagVec[j] && dis[j] < tmpMinDis)
             {
                 v = j;
                 tmpMinDis = dis[j];
             }
         }
         if(v == - || v == Sp)
             return;
         visitFlagVec[v] = true;
         for(int j = ; j <= N; ++ j)
         {
             if(!visitFlagVec[j] && dis[j] > dis[v] + route[v][j])
             {
                 dis[j] = dis[v] + route[v][j];
                 preRoute[j].clear();
                 preRoute[j].push_back(v);
             }
             else if(!visitFlagVec[j] && dis[j] == dis[v] + route[v][j])
                 preRoute[j].push_back(v);
         }
     }
 }
 void dfs(int u)
 {
     if(u == )
     {
         tmpPathVec.push_back(u);
         int tmpBikeNum = , tmpBackBikeNum = ;
         for(int i = ; i < tmpPathVec.size()-; ++i)
         {
             tmpBikeNum += bikeNumStaVec[tmpPathVec[i]]-C/;
             if(tmpBikeNum > )
             {
                 tmpBackBikeNum += tmpBikeNum;
                 tmpBikeNum = ;
             }
         }
         tmpBikeNum = -tmpBikeNum;
         if(tmpBikeNum < dstSendBikeNum)
         {
             dstSendBikeNum = tmpBikeNum;
             dstBackBikeNum = tmpBackBikeNum;
             dstPathVec = tmpPathVec;
         }
         else if(tmpBikeNum == dstSendBikeNum && tmpBackBikeNum < dstBackBikeNum)
         {
             dstPathVec == tmpPathVec;
             dstBackBikeNum = tmpBackBikeNum;
         }
         tmpPathVec.pop_back();
         return;
     }
     tmpPathVec.push_back(u);
     for(auto it = preRoute[u].begin(); it != preRoute[u].end(); ++ it)
         dfs(*it);
     tmpPathVec.pop_back();
 }
 int main()
 {
     cin >> C >> N >> Sp >> M;
     int tmpSt, tmpEnd, tmpDis;
     for(int i = ; i <= N; ++i)
         cin >> bikeNumStaVec[i];
     CLR(route,0x7f);
     CLR(dis,0x7f);
     while(M--)
     {
         cin >> tmpSt >> tmpEnd >> tmpDis;
         route[tmpSt][tmpEnd] = tmpDis;
         route[tmpEnd][tmpSt] = tmpDis;
     }
     dijkstra();
     dfs(Sp);
     cout << dstSendBikeNum;
     reverse(dstPathVec.begin(), dstPathVec.end());
     for(int i = ; i < dstPathVec.size(); ++i)
     {
         if(i == )  printf(" ");
         else        printf("->");
         cout << dstPathVec[i];
     }
     cout << " " << dstBackBikeNum;
     return ;
 }