P1972 [SDOI2009]HH的项链

R65787333

Luogu/P1972/P1972.cpp

@@ -0,0 +1,94 @@
+#include <cctype>
+#include <cstdio>
+
+const int N = 1000005;
+
+int n, q, a[N], pre[N];
+
+// Helpers
+void read(int &);
+
+// Segment Tree
+int cnt, root[N];
+int build(int, int);
+int insert(int, int, int, int, int);
+int query(int, int, int, int);
+
+int main() {
+    read(n);
+    for (int i = 1; i <= n; i++) {
+        read(a[i]);
+    }
+    root[0] = build(1, n);
+    for (int i = 1; i <= n; i++) {
+        if (!pre[a[i]]) {
+            root[i] = insert(root[i - 1], 1, n, i, 1);
+        } else {
+            int tmp = insert(root[i - 1], 1, n, pre[a[i]], -1);
+            root[i] = insert(tmp, 1, n, i, 1);
+        }
+        pre[a[i]] = i;
+    }
+    read(q);
+    while (q--) {
+        int l, r;
+        read(l), read(r);
+        printf("%d\n", query(root[r], 1, n, l));
+    }
+    return 0;
+}
+
+// === Helpers ===
+
+void read(int &x) {
+    x = 0;
+    char ch = getchar();
+    while (!isdigit(ch)) ch = getchar();
+    while (isdigit(ch)) {
+        x = x * 10 + ch - '0';
+        ch = getchar();
+    }
+}
+
+// === Segment Tree ===
+
+struct node {
+    int l, r, c;
+} tr[N << 6];
+
+inline void pushup(int u) {
+    tr[u].c = tr[tr[u].l].c + tr[tr[u].r].c;
+}
+
+int build(int l, int r) {
+    int p = ++cnt;
+    if (l == r) return p;
+    int mid = l + r >> 1;
+    tr[p].l = build(l, mid);
+    tr[p].r = build(mid + 1, r);
+    return p;
+}
+
+int insert(int p, int l, int r, int x, int v) {
+    int q = ++cnt;
+    tr[q] = tr[p];
+    if (l == r) {
+        tr[q].c += v;
+        return q;
+    }
+    int mid = l + r >> 1;
+    if (x <= mid) {
+        tr[q].l = insert(tr[p].l, l, mid, x, v);
+    } else {
+        tr[q].r = insert(tr[p].r, mid + 1, r, x, v);
+    }
+    pushup(q);
+    return q;
+}
+
+int query(int u, int l, int r, int x) {
+    if (l == r) return tr[u].c;
+    int mid = l + r >> 1;
+    if (x <= mid) return tr[tr[u].r].c + query(tr[u].l, l, mid, x);
+    return query(tr[u].r, mid + 1, r, x);
+}