feat(ds/fenwick): O(n) building

Tiphereth-A · Nov 14, 2024 · ef20fcf · ef20fcf
1 parent a62b665
commit ef20fcf
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Showing 3 changed files with 14 additions and 12 deletions.
diff --git a/src/code/ds/fenwick.hpp b/src/code/ds/fenwick.hpp
@@ -12,6 +12,14 @@ class fenwick {
  public:
   //! [1, sz)
   CEXPE fenwick(u32 sz) : a(sz) { assert(sz > 1); }
+  //! [1, sz)
+  CEXP fenwick(spn<T> data) : fenwick((u32)data.size()) {
+    const u32 sz = (u32)data.size();
+    flt_ (u32, i, 1, sz) {
+      a[i] += data[i];
+      if (u32 j = i + bit::lowbit(i); j < sz) a[j] += a[i];
+    }
+  }
 
   //! [pos, sz), pos > 0
   CEXP void add(u32 pos, cT_(T) x) {

diff --git a/src/test_cpverifier/library-checker-datastructure/point_add_range_sum.fenwick.test.cpp b/src/test_cpverifier/library-checker-datastructure/point_add_range_sum.fenwick.test.cpp
@@ -6,12 +6,9 @@ int main() {
   std::cin.tie(nullptr)->std::ios::sync_with_stdio(false);
   u32 n, q;
   std::cin >> n >> q;
-  tifa_libs::ds::fenwick<u64> f(n + 1);
-  u64 x;
-  fle_ (u32, i, 1, n) {
-    std::cin >> x;
-    f.add(i, x);
-  }
+  vecuu a(n + 1);
+  fle_ (u32, i, 1, n) std::cin >> a[i];
+  tifa_libs::ds::fenwick<u64> f(a);
   fle_ (u32, i, 1, q) {
     u32 op, l, r;
     std::cin >> op >> l >> r;

diff --git a/src/test_cpverifier/library-checker-datastructure/static_range_sum.fenwick.test.cpp b/src/test_cpverifier/library-checker-datastructure/static_range_sum.fenwick.test.cpp
@@ -6,12 +6,9 @@ int main() {
   std::cin.tie(nullptr)->std::ios::sync_with_stdio(false);
   u32 n, q;
   std::cin >> n >> q;
-  tifa_libs::ds::fenwick<u64> f(n + 1);
-  u64 x;
-  fle_ (u32, i, 1, n) {
-    std::cin >> x;
-    f.add(i, x);
-  }
+  vecuu a(n + 1);
+  fle_ (u32, i, 1, n) std::cin >> a[i];
+  tifa_libs::ds::fenwick<u64> f(a);
   fle_ (u32, i, 1, q) {
     u32 l, r;
     std::cin >> l >> r;