Subset sum problem (Count)
(Mylib/Typical/subset_sum_count.cpp)

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• Last update: 2021-04-23 23:44:44+09:00

Operations

• subset_sum_count(N, K, a[N])
  • Time complexity $O(NK)$

Requirements

Notes

Problems

References

Code

#pragma once
#include <cassert>
#include <vector>

namespace haar_lib {
  template <typename T>
  auto subset_sum_count(int N, int K, const std::vector<int> &a) {
    assert((int) a.size() == N);
    std::vector<std::vector<T>> dp(2, std::vector<T>(K + 1));

    dp[0][0] = 1;

    for (int i = 0; i < N; ++i) {
      for (int j = 0; j <= K; ++j) {
        if (j >= a[i])
          dp[(i + 1) & 1][j] = dp[i & 1][j - a[i]] + dp[i & 1][j];
        else
          dp[(i + 1) & 1][j] = dp[i & 1][j];
      }
    }

    return dp[N & 1];
  }
}  // namespace haar_lib

#line 2 "Mylib/Typical/subset_sum_count.cpp"
#include <cassert>
#include <vector>

namespace haar_lib {
  template <typename T>
  auto subset_sum_count(int N, int K, const std::vector<int> &a) {
    assert((int) a.size() == N);
    std::vector<std::vector<T>> dp(2, std::vector<T>(K + 1));

    dp[0][0] = 1;

    for (int i = 0; i < N; ++i) {
      for (int j = 0; j <= K; ++j) {
        if (j >= a[i])
          dp[(i + 1) & 1][j] = dp[i & 1][j - a[i]] + dp[i & 1][j];
        else
          dp[(i + 1) & 1][j] = dp[i & 1][j];
      }
    }

    return dp[N & 1];
  }
}  // namespace haar_lib

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