P1975 [国家集训队]排队

https://www.luogu.com.cn/record/97522845

Luogu/P1975/P1975.cpp

@@ -0,0 +1,147 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e4 + 5;
+
+int n, m, h[N], ans;
+std::vector<int> nums;
+
+class SegmentTree {
+  private:
+    struct node {
+        int l, r;
+        int sum;
+
+        node *lchild, *rchild;
+
+        node(const int &_l = 0, const int &_r = 0)
+            : l(_l), r(_r), sum(0), lchild(nullptr), rchild(nullptr) {}
+
+        void pushup() {
+            sum = 0;
+
+            if (lchild != nullptr) sum += lchild->sum;
+            if (rchild != nullptr) sum += rchild->sum;
+        }
+    };
+
+    node *root;
+
+    void modify(node *&cur, int l, int r, int pos, int val) {
+        if (cur == nullptr) cur = new node(l, r);
+
+        if (l == r) {
+            cur->sum += val;
+
+            return;
+        }
+
+        int mid = l + r >> 1;
+
+        if (pos <= mid) modify(cur->lchild, l, mid, pos, val);
+        else modify(cur->rchild, mid + 1, r, pos, val);
+
+        cur->pushup();
+    }
+
+    int query(node *cur, int l, int r, int ql, int qr) {
+        if (cur == nullptr) return 0;
+        if (ql <= l && r <= qr) return cur->sum;
+
+        int mid = l + r >> 1,
+            res = 0;
+
+        if (ql <= mid) res += query(cur->lchild, l, mid, ql, qr);
+        if (qr > mid) res += query(cur->rchild, mid + 1, r, ql, qr);
+
+        return res;
+    }
+
+  public:
+    SegmentTree()
+        : root(nullptr) {}
+
+    void modify(int pos, int val) {
+        modify(root, 1, n, pos, val);
+    }
+
+    int query(int ql, int qr) {
+        return query(root, 1, n, ql, qr);
+    }
+} tr[N];
+
+int lowbit(int x) {
+    return x & -x;
+}
+
+void add(int x, int y, int z) {
+    for (; x <= n; x += lowbit(x)) tr[x].modify(y, z);
+}
+
+int sum(int x, int l, int r) {
+    int res = 0;
+
+    for (; x; x -= lowbit(x)) res += tr[x].query(l, r);
+
+    return res;
+}
+
+int get(int x) {
+    return sum(x - 1, h[x] + 1, n) + sum(n, 1, h[x] - 1) - sum(x - 1, 1, h[x] - 1);
+}
+
+int find(int x) {
+    return std::lower_bound(nums.begin(), nums.end(), x) - nums.begin() + 1;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> h[i];
+
+        nums.emplace_back(h[i]);
+    }
+
+    std::sort(nums.begin(), nums.end());
+    std::transform(h + 1, h + 1 + n, h + 1, find);
+
+    for (int i = 1; i <= n; i++) {
+        add(i, h[i], 1);
+        ans += sum(i - 1, h[i] + 1, n);
+    }
+
+    cout << ans << endl;
+
+    cin >> m;
+
+    while (m--) {
+        int x, y;
+
+        cin >> x >> y;
+
+        if (x > y) std::swap(x, y);
+        if (h[x] > h[y]) ans++;
+
+        ans -= get(x) + get(y);
+        add(x, h[x], -1);
+        add(y, h[y], -1);
+        std::swap(h[x], h[y]);
+        if (h[x] > h[y]) ans--;
+        add(x, h[x], 1);
+        add(y, h[y], 1);
+        ans += get(x) + get(y);
+
+        cout << ans << endl;
+    }
+
+    return 0;
+}