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fenwick_tree O(n) init #170

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0cbde95
fenwick_tree O(n) init
alantudyk Sep 27, 2023
657d3f0
minus 2 unnecessary iterations
alantudyk Sep 27, 2023
e56e39d
spirit of modern C++
alantudyk Oct 2, 2023
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spirit of modern C++
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@alantudyk
alantudyk committed Oct 2, 2023
commit e56e39dc5e7ab767092f4993ced113202f4dce61
6 changes: 4 additions & 2 deletions atcoder/fenwicktree.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,15 +15,17 @@ template <class T> struct fenwick_tree {
public:
fenwick_tree() : _n(0) {}
explicit fenwick_tree(int n) : _n(n), data(n) {}
explicit fenwick_tree(const std::vector<T> &v) : _n(v.size()), data(v.size()) {
explicit fenwick_tree(const T *const a, const int len) : fenwick_tree(len) {
U p = 0;
int i, j = -1;
while (++j < _n)
data[j] = p += U(v[j]);
data[j] = p += U(a[j]);
while (--j > 1)
if ((i = j & (j + 1)) > 0)
data[j] -= data[i - 1];
}
explicit fenwick_tree(const std::vector<T> &v) :
fenwick_tree(v.data(), int(v.size())) {}

void add(int p, T x) {
assert(0 <= p && p < _n);
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