pat 1018. Public Bike Management （dijkstra+dfs）

最短路问题，复习dijkstra和dfs

首先dijkstra求出最短路，然后dfs求出所有路径

求出路径中send最小的，再求其中back最小的

point：题设的要求是修正最短路径上的所有点，实际上必须严格遵循访问顺序修改每个点的权值（eg:要依次修改权值分别为3，10的两个点，必须send2back5而非简单地back3)，亦即到达目标点sp后的回程是不能修改的。

如果错误地理解为简单地将最短路径上的所有点上的权值全部改为half-full的话，会有两个case过不了

#include<stdio.h>#include<iostream>#include<stack>#include<map>#include<string>#include<algorithm>using namespace std;int cmax,n,sp,m,longest;const int MAX=0x7fffffff;const int number=510;int in[number];int ld[number][number];int dis[number];int bl[number];int pre[number];int change[number];stack<int> sta;multimap<int,string> mp;multimap<int,string> mp2;multimap<int,string>::iterator mi;int used[number];int mm=MAX;int minsum=MAX;string itos(int num){string s="";if(num<10){s=" ";s[0]=(num+'0');}    if(num>=10&&num<=99){s="  ";s[0]=(num%10+'0');s[1]=(num/10+'0');}if(num>=100){s="   ";s[0]=(num%10+'0');s[1]=((num/10)%10+'0');s[2]=(num/100+'0');}    return s;}void dijkstra(int start)    {int min,i,u,j;bl[start]=1;for(i=1; i<=n; ++i){dis[i]=ld[start][i];if(dis[i] == MAX)pre[i] = -1;elsepre[i] = start;}    for(i=1; i<=n; i++){min=MAX;u=start;for(j=1;j<=n;j++)if(dis[j]<min&&!bl[j]){min=dis[j];u=j;}bl[u]=1;for(j=1;j<=n;j++)if(ld[u][j]<MAX&&!bl[j]){if(dis[u]+ld[u][j]<dis[j]){dis[j]=dis[u]+ld[u][j];pre[j]=u;}}}}void display(){    stack<int> stmp=sta,stmp2;int x=0,sum=0,store=0;string str="";while(!stmp.empty()){x=stmp.top();stmp.pop();if(x==0)break;str+=itos(x);str+=">-";stmp2.push(change[x]);}while(!stmp2.empty()){x=stmp2.top();stmp2.pop();if(x>=0) {store+=x; }else{if(-x<=store){store+=x;}else{ sum+=(-x-store);store=0;}}}str+="0";reverse(str.begin(),str.end());    if(sum>0){if(sum==minsum){mp.insert(make_pair(store,str));}if(sum<minsum){mp.clear();mp.insert(make_pair(store,str));minsum=sum;}}else mp2.insert(make_pair(store,str)); }void dfs(int start,int l){int rd=0,i,u;sta.push(start);if(l>longest) {sta.pop();return; }if(start==sp&&l==longest){  mm=l;display();sta.pop();return;}u=start;    for(i=1;i<=n;i++){if(ld[u][i]<=longest&&!used[i]&&u!=i){used[i]=1;dfs(i,l+ld[u][i]);used[i]=0;}}sta.pop();}int main(){    int i,j,s1,s2,t;   scanf("%d %d %d %d",&cmax,&n,&sp,&m);for(i=0;i<=n;i++)for(j=0;j<=n;j++)ld[i][j]=MAX;ld[0][0]=0;for(i=1;i<=n;i++){scanf("%d",&in[i]);ld[i][i]=0;}for(i=0;i<m;i++){scanf("%d %d %d",&s1,&s2,&t);ld[s1][s2]=t;ld[s2][s1]=t;}for(i=1;i<=n;i++){change[i]=in[i]-(cmax/2);}dijkstra(0);longest=dis[sp];dfs(0,0);if(!mp2.empty())cout<<"0 "<<mp2.begin()->second<<" "<<mp2.begin()->first<<endl;elsecout<<minsum<<" "<<mp.begin()->second<<" "<<mp.begin()->first<<endl;return 0;}