UVALive 6511 Term Project

Term Project

Time Limit: 3000ms

Memory Limit: 131072KB

This problem will be judged on UVALive. Original ID: 6511
64-bit integer IO format: %lld      Java class name: Main

 

 

解题：强连通分量 

 #include <bits/stdc++.h>
 using namespace std;
 const int maxn = ;
 struct arc{
     int to,next;
     arc(int x = ,int y = -){
         to = x;
         next = y;
     }
 }e[maxn*];
 int head[maxn],dfn[maxn],low[maxn],belong[maxn],cnt[maxn];
 int tot,clk,scc;
 bool instack[maxn];
 stack<int>stk;
 void init(){
     for(int i = tot = clk = scc = ; i < maxn; ++i){
         head[i] = -;
         dfn[i] = ;
         cnt[i] = belong[i] = ;
         instack[i] = false;
     }
     while(!stk.empty()) stk.pop();
 }
 void add(int u,int v){
     e[tot] = arc(v,head[u]);
     head[u] = tot++;
 }
 void tarjan(int u){
     dfn[u] = low[u] = ++clk;
     instack[u] = true;
     stk.push(u);
     for(int i = head[u]; ~i; i = e[i].next){
         if(!dfn[e[i].to]){
             tarjan(e[i].to);
             low[u] = min(low[u],low[e[i].to]);
         }else if(instack[e[i].to]) low[u] = min(low[u],dfn[e[i].to]);
     }
     if(low[u] == dfn[u]){
         scc++;
         int v;
         do{
             instack[v = stk.top()] = false;
             belong[v] = scc;
             stk.pop();
             cnt[scc]++;
         }while(v != u);
     }
 }
 int main(){
     int kase,n;
     scanf("%d",&kase);
     while(kase--){
         init();
         scanf("%d",&n);
         int ret = ;
         for(int i = ,tmp; i <= n; ++i){
             scanf("%d",&tmp);
             add(i,tmp);
             ret += i == tmp;
         }
         for(int i = ; i <= n; ++i)
             if(!dfn[i]) tarjan(i);
         for(int i = ; i <= scc; ++i)
             if(cnt[i] > ) ret += cnt[i];
         printf("%d\n",n - ret);
     }
     return ;
 }