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2240. Number of Ways to Buy Pens and Pencils 👍

  • Time: $O(\frac{\texttt{total}}{\texttt{cost1}})$
  • Space: $O(1)$
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class Solution {
 public:
  long long waysToBuyPensPencils(int total, int cost1, int cost2) {
    long ans = 0;
    const int maxPen = total / cost1;

    for (int i = 0; i <= maxPen; ++i)
      ans += (total - i * cost1) / cost2 + 1;

    return ans;
  }
};

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class Solution {
  public long waysToBuyPensPencils(int total, int cost1, int cost2) {
    long ans = 0;
    final int maxPen = total / cost1;

    for (int i = 0; i <= maxPen; ++i)
      ans += (total - i * cost1) / cost2 + 1;

    return ans;
  }
}

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class Solution:
  def waysToBuyPensPencils(self, total: int, cost1: int, cost2: int) -> int:
    maxPen = total // cost1
    return sum((total - i * cost1) // cost2
               for i in range(maxPen + 1)) + maxPen + 1