环

题面

先粘上gouzhi的题面

题解

处理出置换中的所有轮换，瞎jb打就OK了

代码

#include<cstdio>
#include<vector> 
#include<algorithm> 
const int maxn = 500007;
using std::vector;
inline int read() { 
    int x = 0; 
    char c = getchar(); 
    while(c < '0' || c > '9') c = getchar(); 
    while(c <= '9' && c >= '0')x = x * 10 + c - '0',c = getchar();
    return x; 
}
int a[maxn],bel[maxn],loc[maxn],num = 0,cnt; bool hav[maxn],vis[maxn];  
vector<int>vec[maxn]; 
void dfs(int tx,int fa) { 
    loc[tx] = ++num; 
    vec[cnt].push_back(tx); bel[tx] = cnt; 
    if(a[tx] == fa) return; 
    dfs(a[tx],fa); 
}   
void solve(int x,int m) { 
    int B = bel[x]; 
    int size = vec[B].size(); 
    int ans_loc = (m + loc[x]) % size; 
    //if(!ans_loc)ans_loc = 1;
    printf("%d\n",vec[B][ans_loc]); 
} 
int main() { 
    freopen("kengdie.in","r",stdin); 
    freopen("kengdie.out","w",stdout); 
    int n = 0; 
    for(n = 1;;++ n) { 
        a[n] = read(); 
        if(hav[a[n]]) break;hav[a[n]] = true;   
    } 
    for(int i = 1;i < n;++ i) { 
        //vec[i].push_back(); 
        if(!bel[i]) { 
            num = -1; bel[i] = ++ cnt; 
            dfs(i,i);   
        } 
    }   
    int x = a[n],m = read();    
    solve(x,m);
    while(scanf("%d%d",&x,&m) == 2) 
        solve(x,m); 
    return 0;
}