P1383 高级打字机

R65866648

Luogu/P1383/P1383.cpp

@@ -0,0 +1,77 @@
+#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);
+}