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 = 100010;
struct arc{
    int to,next;
    arc(int x = 0,int y = -1){
        to = x;
        next = y;
    }
}e[maxn*10];
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 = 0; i < maxn; ++i){
        head[i] = -1;
        dfn[i] = 0;
        cnt[i] = belong[i] = 0;
        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 = 0;
        for(int i = 1,tmp; i <= n; ++i){
            scanf("%d",&tmp);
            add(i,tmp);
            ret += i == tmp;
        }
        for(int i = 1; i <= n; ++i)
            if(!dfn[i]) tarjan(i);
        for(int i = 1; i <= scc; ++i)
            if(cnt[i] > 1) ret += cnt[i];
        printf("%d
",n - ret);
    }
    return 0;
}