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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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fenwick_tree O(n) init
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@alantudyk
alantudyk committed Sep 27, 2023
commit 0cbde952f3fda839b2e9eb4ceb33535c543cb34b
9 changes: 9 additions & 0 deletions atcoder/fenwicktree.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,15 @@ 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()) {
U p = 0;
int i, j = -1;
while (++j < _n)
data[j] = p += U(v[j]);
while (--j >= 0)
if ((i = j & (j + 1)) > 0)
data[j] -= data[i - 1];
}

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