[ABC167D] Teleporter
一眼有循环节，然后就秒了。
#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 2e5 + 10;
int n, k, a[N], vis[N], xhj = 0;
pair <int, int> bs[N];
signed main() {
cin >> n >> k;
for(int i = 1; i <= n; i++) cin >> a[i];
int now = 1, qd = 0;
if(k <= n) {
while(k--) {
now = a[now];
}
cout<<now;
return 0;
}
for(int i = 1; i <= n; i++) {
if(!vis[now]) vis[now] = 1, bs[now].first = i;
else if(vis[now]) {
qd = now;
bs[now].second = i;
xhj = i - bs[now].first;
break;
}
now = a[now];
}
now = 1;
while(now != qd) {
now = a[now]; k--;
}
k %= xhj;
while(k--) {
now = a[now];
}
cout << now;
}