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OI-codes/Luogu/P1383/P1383.cpp

85 lines
1.6 KiB
C++

#include <iostream>
using std::cin;
using std::cout;
using std::endl;
// Limits
const int N = 100005;
// Variables
int n;
char op;
// Persistent Segment Tree
int p, cnt, root[N];
int insert(int, int, int, int);
int query(int, int, int, int);
int main() {
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> op;
if (op == 'T') {
char x;
cin >> x;
int k = x - 'a';
root[p + 1] = insert(root[p], 1, n, k);
p++;
} else if (op == 'U') {
int x;
cin >> x;
root[p + 1] = root[std::max(p - x, 0)];
p++;
} else {
int x;
cin >> x;
cout << char(query(root[p], 1, n, x) + 'a') << endl;
}
}
return 0;
}
// Persistent Segment Tree
struct node {
int l, r, s, d;
node()
: l(0),
r(0),
s(0),
d(0) {}
node(int _l, int _r)
: l(_l),
r(_r),
s(0),
d(0) {}
} tr[N << 5];
int insert(int p, int l, int r, int x) {
int q = ++cnt;
tr[q] = tr[p];
if (l == r) {
tr[q].s = 1;
tr[q].d = x;
return q;
}
int mid = l + r >> 1;
if (tr[tr[q].l].s < mid - l + 1) {
tr[q].l = insert(tr[q].l, l, mid, x);
} else {
tr[q].r = insert(tr[q].r, mid + 1, r, x);
}
tr[q].s = tr[tr[q].l].s + tr[tr[q].r].s;
return q;
}
int query(int p, int l, int r, int x) {
if (l == r) return tr[p].d;
int mid = l + r >> 1;
if (x <= mid) return query(tr[p].l, l, mid, x);
return query(tr[p].r, mid + 1, r, x);
}