test/aoj/ALDS1_5_D/main.test.cpp
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Code
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D"
#include <functional>
#include <iostream>
#include <vector>
#include "Mylib/IO/input_vector.cpp"
#include "Mylib/Typical/inversion_number.cpp"
namespace hl = haar_lib;
int main() {
int n;
std::cin >> n;
auto a = hl::input_vector<int>(n);
auto ans = hl::inversion_number(a, std::greater<int>());
std::cout << ans << std::endl;
return 0;
}
#line 1 "test/aoj/ALDS1_5_D/main.test.cpp"
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D"
#include <functional>
#include <iostream>
#include <vector>
#line 4 "Mylib/IO/input_vector.cpp"
namespace haar_lib {
template <typename T>
std::vector<T> input_vector(int N) {
std::vector<T> ret(N);
for (int i = 0; i < N; ++i) std::cin >> ret[i];
return ret;
}
template <typename T>
std::vector<std::vector<T>> input_vector(int N, int M) {
std::vector<std::vector<T>> ret(N);
for (int i = 0; i < N; ++i) ret[i] = input_vector<T>(M);
return ret;
}
} // namespace haar_lib
#line 2 "Mylib/Typical/inversion_number.cpp"
#include <cstdint>
#line 4 "Mylib/Typical/inversion_number.cpp"
namespace haar_lib {
namespace inversion_number_impl {
template <typename T, typename Compare>
int64_t rec(std::vector<T> &a, const Compare &compare) {
const int n = a.size();
if (n <= 1) return 0;
int64_t ret = 0;
std::vector<T> b(a.begin(), a.begin() + n / 2);
std::vector<T> c(a.begin() + n / 2, a.end());
ret += rec(b, compare);
ret += rec(c, compare);
int ai = 0, bi = 0, ci = 0;
while (ai < n) {
if (bi < (int) b.size() and (ci == (int) c.size() or not compare(b[bi], c[ci]))) {
a[ai] = b[bi];
++bi;
} else {
ret += n / 2 - bi;
a[ai] = c[ci];
++ci;
}
++ai;
}
return ret;
}
} // namespace inversion_number_impl
template <typename T, typename Compare>
int64_t inversion_number(std::vector<T> a, const Compare &compare) {
return inversion_number_impl::rec(a, compare);
}
} // namespace haar_lib
#line 8 "test/aoj/ALDS1_5_D/main.test.cpp"
namespace hl = haar_lib;
int main() {
int n;
std::cin >> n;
auto a = hl::input_vector<int>(n);
auto ans = hl::inversion_number(a, std::greater<int>());
std::cout << ans << std::endl;
return 0;
}
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