P3919 【模板】可持久化线段树 1（可持久化数组）

https://www.luogu.com.cn/record/94757324

Luogu/P3919/P3919.cpp

@@ -0,0 +1,100 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n, m, a[N], root[N], cnt;
+
+struct node {
+    int l, r, v;
+} tr[N << 6];
+
+int build(int l, int r) {
+    int p = ++cnt;
+
+    if (l == r) {
+        tr[p].v = a[l];
+
+        return p;
+    }
+
+    int mid = l + r >> 1;
+
+    tr[p].l = build(l, mid);
+    tr[p].r = build(mid + 1, r);
+
+    return p;
+}
+
+int modify(int u, int l, int r, int p, int v) {
+    int q = ++cnt;
+
+    tr[q] = tr[u];
+
+    if (l == r) {
+        a[p] = v;
+        tr[q].v = v;
+
+        return q;
+    }
+
+    int mid = l + r >> 1;
+
+    if (p <= mid) {
+        tr[q].l = modify(tr[u].l, l, mid, p, v);
+    } else {
+        tr[q].r = modify(tr[u].r, mid + 1, r, p, v);
+    }
+
+    return q;
+}
+
+int query(int u, int l, int r, int p) {
+    if (l == r) return tr[u].v;
+
+    int mid = l + r >> 1;
+
+    if (p <= mid) {
+        return query(tr[u].l, l, mid, p);
+    }
+
+    return query(tr[u].r, mid + 1, r, p);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    root[0] = build(1, n);
+
+    for (int i = 1, ver, op; i <= m; i++) {
+        cin >> ver >> op;
+
+        if (op == 1) {
+            int p, v;
+
+            cin >> p >> v;
+
+            root[i] = modify(root[ver], 1, n, p, v);
+        } else {  // op == 2
+            int p;
+
+            cin >> p;
+
+            cout << query(root[ver], 1, n, p) << endl;
+
+            root[i] = root[ver];
+        }
+    }
+
+    return 0;
+}