bit/k_subset.hpp

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Last update: 2024-11-09 00:49:07+00:00
Include: #include "bit/k_subset.hpp"

Depends on

Verified with

test/bit/k_subset.test.cpp

Code

#pragma once
#include "bit/ctz.hpp"

template <class F>
void k_subset(int n, int k, F f = F()) {
  if (k == 0) return f(0), void();
  for (int mask = (1 << k) - 1; mask < 1 << n;) {
    f(mask);
    int lsb = mask & -mask;
    mask += lsb;
    int d = ctz(mask) - ctz(lsb) - 1;
    mask |= (1 << d) - 1;
  }
}

#line 2 "prelude.hpp"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using vc = vector<char>;
#define rep2(i, m, n) for (auto i = (m); i < (n); i++)
#define rep(i, n) rep2(i, 0, n)
#define repr2(i, m, n) for (auto i = (n); i-- > (m);)
#define repr(i, n) repr2(i, 0, n)
#define all(x) begin(x), end(x)
auto ndvec(int n, auto e) { return vector(n, e); }
auto ndvec(int n, auto ...e) { return vector(n, ndvec(e...)); }
auto comp_key(auto&& f) { return [&](auto&& a, auto&& b) { return f(a) < f(b); }; }
auto& max(const auto& a, const auto& b) { return a < b ? b : a; }
auto& min(const auto& a, const auto& b) { return b < a ? b : a; }
#if __cpp_lib_ranges
namespace R = std::ranges;
namespace V = std::views;
#endif
#line 3 "bit/ctz.hpp"

#pragma GCC target("bmi")

template <class T>
int ctz(T x) {
  if (!x) return sizeof(T) * 8;
  if constexpr (sizeof(T) <= sizeof(unsigned)) {
    return __builtin_ctz((unsigned)x);
  } else if constexpr (sizeof(T) <= sizeof(unsigned long long)) {
    return __builtin_ctzll((unsigned long long)x);
  } else if constexpr (sizeof(T) <= sizeof(unsigned long long) * 2) {
    unsigned long long y = x;
    return y ? ctz(y)
             : sizeof(y) * 8 + ctz((unsigned long long)(x >> sizeof(y) * 8));
  }
}
#line 3 "bit/k_subset.hpp"

template <class F>
void k_subset(int n, int k, F f = F()) {
  if (k == 0) return f(0), void();
  for (int mask = (1 << k) - 1; mask < 1 << n;) {
    f(mask);
    int lsb = mask & -mask;
    mask += lsb;
    int d = ctz(mask) - ctz(lsb) - 1;
    mask |= (1 << d) - 1;
  }
}