UVALive 6511 Term Project

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 100010;
 4 struct arc{
 5     int to,next;
 6     arc(int x = 0,int y = -1){
 7         to = x;
 8         next = y;
 9     }
10 }e[maxn*10];
11 int head[maxn],dfn[maxn],low[maxn],belong[maxn],cnt[maxn];
12 int tot,clk,scc;
13 bool instack[maxn];
14 stack<int>stk;
15 void init(){
16     for(int i = tot = clk = scc = 0; i < maxn; ++i){
17         head[i] = -1;
18         dfn[i] = 0;
19         cnt[i] = belong[i] = 0;
20         instack[i] = false;
21     }
22     while(!stk.empty()) stk.pop();
23 }
24 void add(int u,int v){
25     e[tot] = arc(v,head[u]);
26     head[u] = tot++;
27 }
28 void tarjan(int u){
29     dfn[u] = low[u] = ++clk;
30     instack[u] = true;
31     stk.push(u);
32     for(int i = head[u]; ~i; i = e[i].next){
33         if(!dfn[e[i].to]){
34             tarjan(e[i].to);
35             low[u] = min(low[u],low[e[i].to]);
36         }else if(instack[e[i].to]) low[u] = min(low[u],dfn[e[i].to]);
37     }
38     if(low[u] == dfn[u]){
39         scc++;
40         int v;
41         do{
42             instack[v = stk.top()] = false;
43             belong[v] = scc;
44             stk.pop();
45             cnt[scc]++;
46         }while(v != u);
47     }
48 }
49 int main(){
50     int kase,n;
51     scanf("%d",&kase);
52     while(kase--){
53         init();
54         scanf("%d",&n);
55         int ret = 0;
56         for(int i = 1,tmp; i <= n; ++i){
57             scanf("%d",&tmp);
58             add(i,tmp);
59             ret += i == tmp;
60         }
61         for(int i = 1; i <= n; ++i)
62             if(!dfn[i]) tarjan(i);
63         for(int i = 1; i <= scc; ++i)
64             if(cnt[i] > 1) ret += cnt[i];
65         printf("%d\n",n - ret);
66     }
67     return 0;
68 }