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concave-min-plus-convolution.hpp
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concave-min-plus-convolution.hpp
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#pragma once
#include <vector>
using namespace std;
#include "monotone-minima.hpp"
// a は下に凸, b は自由
template <typename T>
vector<T> concave_min_plus_convolution(const vector<T>& a, const vector<T>& b) {
if (a.empty() or b.empty()) return {};
int n = a.size(), m = b.size();
auto argmin = monotone_minima(n + m - 1, m, [&](int i, int j, int k) {
if (i < k) return true;
if (i - j >= n) return false;
return a[i - j] + b[j] <= a[i - k] + b[k];
});
vector<T> ans(n + m - 1);
for (int i = 0; i < n + m - 1; i++) {
int j = argmin[i];
ans[i] = a[i - j] + b[j];
}
return ans;
}
// a は上に凸, b は自由
template <typename T>
vector<T> concave_max_plus_convolution(const vector<T>& a, const vector<T>& b) {
if (a.empty() or b.empty()) return {};
int n = a.size(), m = b.size();
auto argmin = monotone_minima(n + m - 1, m, [&](int i, int j, int k) {
if (i < k) return true;
if (i - j >= n) return false;
return a[i - j] + b[j] >= a[i - k] + b[k];
});
vector<T> ans(n + m - 1);
for (int i = 0; i < n + m - 1; i++) {
int j = argmin[i];
ans[i] = a[i - j] + b[j];
}
return ans;
}