NYOJ 247虚拟城市之旅(强连通缩点 + 搜索)

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题目连接:http://acm.nyist.edu.cn/JudgeOnline/problem.php?pid=247

分析:为了解决环的问题,可以进行强连通缩点建图,可以记录一下每个强连通中商品能达到的最大值和最小值,然后在缩过点的无环图上搜索,在搜索路径上不断更新商品最小值与最大差值,如果能到达终点更新最大利润。

参考代码如下:

 #include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>#include <algorithm>using namespace std;#define NN 100005#define MM 1000005#define CLR(arr,v) memset(arr,v,sizeof(arr))int Connect[NN],Price[NN],ConnectNum,H[NN],Num[MM],Next[MM],Low[NN],First[NN],Stack[NN],top;bool InStack[NN];int Min[NN],Max[NN];int pos,ind,result;int h[NN],num[MM],nex[MM];void Clear(){result = 0;pos = 0;CLR(h,-1);CLR(H,-1); CLR(InStack,0);CLR(Max,-1);fill(Min,Min+NN,10000);}void add1(int u,int v){Num[pos] = v;Next[pos] = H[u];H[u] = pos++;}void add2(int u,int v){num[pos] = v;nex[pos] = h[u];h[u] = pos++;}void Dfs(int cur){First[cur] = Low[cur] = ++ind;Stack[top++] = cur;InStack[cur] = true;for(int i = H[cur];i != -1;i = Next[i]){if(!First[ Num[i] ]){Dfs(Num[i]);Low[cur] = min(Low[cur],Low[ Num[i] ]);}else if(InStack[ Num[i] ])Low[cur] = min(Low[cur],First[ Num[i]]);}if(Low[cur] == First[cur]){int s;ConnectNum++;do{s = Stack[--top];InStack[s] = false;Connect[s] = ConnectNum;Min[ConnectNum] = min(Min[ConnectNum],Price[s]);Max[ConnectNum] = max(Max[ConnectNum],Price[s]);}while(s != cur);}}int Tarjan(int n){ConnectNum = 0;ind = top = 0;CLR(First,0);CLR(Low,0);for(int i = 1;i <= n;++i){if(!First[i]) Dfs(i);}return ConnectNum;}void Builtgraph(int n){pos = 0;for(int i = 1;i <= n;++i)for(int j = H[i];j != -1;j = Next[j])if(Connect[i] != Connect[ Num[j] ])add2(Connect[i],Connect[ Num[j] ]);}void dfs(int cur,int n,int Mnum,int MaxNum){int maxres = 0;if(cur == n) {result = max(result,MaxNum);return ;}for(int i = h[cur];i != -1;i = nex[i]){maxres = max(MaxNum,max(Max[ num[i] ] - Mnum,Max[ num[i] ] - Min[ num[i] ]));dfs(num[i],n,min(Mnum,Min[ num[i] ]),maxres);}}int main(){//freopen("2.txt","r",stdin);int m,n;  int T = 1;while(scanf("%d%d",&n,&m) != EOF){Clear();int z,b,e;for(int i = 1;i <= n;++i)scanf("%d",&Price[i]);for(int i = 0;i < m;++i){scanf("%d%d%d",&b,&e,&z);add1(b,e);if(z == 2) add1(e,b);}// T++;if(T >= 4) continue;Tarjan(n);Builtgraph(n);dfs(Connect[1],Connect[n],Min[ Connect[1] ],Max[ Connect[1] ] - Min [ Connect[1] ]);printf("%d\n",result);}return 0;}        


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