From 54795c85ded34b7f338a55a6726346783e62343d Mon Sep 17 00:00:00 2001 From: Reznov <78517110+alantudyk@users.noreply.github.com> Date: Wed, 27 Sep 2023 01:59:47 +0300 Subject: [PATCH 1/3] BIT O(n) init --- segmenttree/binary_indexed_tree.hpp | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/segmenttree/binary_indexed_tree.hpp b/segmenttree/binary_indexed_tree.hpp index 88ace04b..fca19855 100644 --- a/segmenttree/binary_indexed_tree.hpp +++ b/segmenttree/binary_indexed_tree.hpp @@ -8,6 +8,16 @@ template struct BIT { int n; std::vector data; BIT(int len = 0) : n(len), data(len) {} + BIT(const std::vector &v) : n(v.size()), data(v.size()) { + T p = 0; + for (int i = 0; i < n; i++) { + data[i] = p += v[i]; + } + for (int j = n - 1; j >= 0; j--) { + const int i = j & (j + 1); + if (i > 0) data[j] -= data[i - 1]; + } + } void reset() { std::fill(data.begin(), data.end(), T(0)); } void add(int pos, T v) { // a[pos] += v pos++; From 5997d20a9d00995f56de0d028fdc0663163683ba Mon Sep 17 00:00:00 2001 From: Reznov <78517110+alantudyk@users.noreply.github.com> Date: Wed, 27 Sep 2023 19:51:25 +0300 Subject: [PATCH 2/3] minus 2 unnecessary iterations --- segmenttree/binary_indexed_tree.hpp | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/segmenttree/binary_indexed_tree.hpp b/segmenttree/binary_indexed_tree.hpp index fca19855..61345bda 100644 --- a/segmenttree/binary_indexed_tree.hpp +++ b/segmenttree/binary_indexed_tree.hpp @@ -13,7 +13,7 @@ template struct BIT { for (int i = 0; i < n; i++) { data[i] = p += v[i]; } - for (int j = n - 1; j >= 0; j--) { + for (int j = n - 1; j > 1; j--) { const int i = j & (j + 1); if (i > 0) data[j] -= data[i - 1]; } From ef421ee468fe9e2e2990e91bf8ab75420001c51e Mon Sep 17 00:00:00 2001 From: Reznov <78517110+alantudyk@users.noreply.github.com> Date: Tue, 3 Oct 2023 00:12:52 +0300 Subject: [PATCH 3/3] spirit of modern C++ --- segmenttree/binary_indexed_tree.hpp | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/segmenttree/binary_indexed_tree.hpp b/segmenttree/binary_indexed_tree.hpp index 61345bda..0107b6e1 100644 --- a/segmenttree/binary_indexed_tree.hpp +++ b/segmenttree/binary_indexed_tree.hpp @@ -8,16 +8,17 @@ template struct BIT { int n; std::vector data; BIT(int len = 0) : n(len), data(len) {} - BIT(const std::vector &v) : n(v.size()), data(v.size()) { + BIT(const T *const a, const int len) : BIT(len) { T p = 0; for (int i = 0; i < n; i++) { - data[i] = p += v[i]; + data[i] = p += a[i]; } for (int j = n - 1; j > 1; j--) { const int i = j & (j + 1); if (i > 0) data[j] -= data[i - 1]; } } + BIT(const std::vector &v) : BIT(v.data(), int(v.size())) {} void reset() { std::fill(data.begin(), data.end(), T(0)); } void add(int pos, T v) { // a[pos] += v pos++; pFad - Phonifier reborn

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