Number of ways to buy pens and pencils

We will loop over the pens and pencils and add the start and end points to a list. Then we will sort the list and loop over it. We will keep track of the current color and the current start point. When we reach a new color, we will add the current color and the current start point to the result. Then we will update the current color and the current start point.

class Solution:
    def waysToBuyPensPencils(self, total: int, cost1: int, cost2: int) -> int:
        cost1, cost2 = max(cost1, cost2), min(cost1, cost2)
        res = 0
        for i in range(1+total // cost1):
            left = max(total-i*cost1, 0)
            res += 1+left // cost2
        return res

Time complexity: O(n)
Space complexity: O(1)