P3834 【模板】可持久化线段树 2

https://www.luogu.com.cn/record/91986713

Luogu/P3834/P3834.cpp

@@ -4,88 +4,87 @@
 
 using std::cin;
 using std::cout;
-using std::endl;
+const char endl = '\n';
 
-const int N = 200005;
+const int N = 2e5 + 5;
 
-int n, m, l, r, k, a[N];
+int n, m, a[N];
-std::vector<int> nums;
-
-// Helpers
-int find(int);
-
-// Segment Tree
 int cnt, root[N];
-int build(int, int);
+std::vector<int> nums;
-int insert(int, int, int, int);
-int query(int, int, int, int, int);
-
-int main() {
-    cin >> n >> m;
-    for (int i = 1; i <= n; i++) {
-        cin >> a[i];
-        nums.push_back(a[i]);
-    }
-    std::sort(nums.begin(), nums.end());
-    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
-    root[0] = build(0, nums.size() - 1);
-    for (int i = 1; i <= n; i++) {
-        root[i] = insert(root[i - 1], 0, nums.size() - 1, find(a[i]));
-    }
-    while (m--) {
-        cin >> l >> r >> k;
-        cout << nums[query(root[r], root[l - 1], 0, nums.size() - 1, k)] << endl;
-    }
-    return 0;
-}
-
-// === Helpers ===
-
-inline int find(int x) {
-    return std::lower_bound(nums.begin(), nums.end(), x) - nums.begin();
-}
-
-// === Segment Tree ===
 
 struct node {
     int l, r, c;
-
-    node()
-        : l(0),
-          r(0),
-          c(0) {}
 } tr[N << 5];
 
 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 q = ++cnt;
     tr[q] = tr[p];
+
     if (l == r) {
         tr[q].c++;
         return q;
     }
+
     int mid = l + r >> 1;
-    if (x <= mid) {
+
-        tr[q].l = insert(tr[p].l, l, mid, x);
+    if (x <= mid) tr[q].l = insert(tr[q].l, l, mid, x);
-    } else {
+    else tr[q].r = insert(tr[q].r, mid + 1, r, x);
-        tr[q].r = insert(tr[p].r, mid + 1, r, x);
+
-    }
     tr[q].c = tr[tr[q].l].c + tr[tr[q].r].c;
+
     return q;
 }
 
-int query(int q, int p, int l, int r, int k) {
+int query(int p, int q, int l, int r, int x) {
     if (l == r) return l;
-    int c = tr[tr[q].l].c - tr[tr[p].l].c;
+    int c = tr[tr[p].l].c - tr[tr[q].l].c;
     int mid = l + r >> 1;
-    if (k <= c) return query(tr[q].l, tr[p].l, l, mid, k);
+
-    return query(tr[q].r, tr[p].r, mid + 1, r, k - c);
+    if (x <= c) return query(tr[p].l, tr[q].l, l, mid, x);
+    return query(tr[p].r, tr[q].r, mid + 1, r, x - c);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        nums.emplace_back(a[i]);
+    }
+
+    std::sort(nums.begin(), nums.end());
+    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
+
+    root[0] = build(0, nums.size() - 1);
+
+    for (int i = 1; i <= n; i++) {
+        root[i] = insert(root[i - 1], 0, nums.size() - 1, std::lower_bound(nums.begin(), nums.end(), a[i]) - nums.begin());
+    }
+
+    while (m--) {
+        int l, r, k;
+
+        cin >> l >> r >> k;
+
+        cout << nums.at(query(root[r], root[l - 1], 0, nums.size() - 1, k)) << endl;
+    }
+
+    return 0;
 }