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Simplify climbing stairs and use constant memory #6628

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Oct 30, 2022
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29 changes: 14 additions & 15 deletions dynamic_programming/climbing_stairs.py
Original file line number Diff line number Diff line change
@@ -1,20 +1,20 @@
#!/usr/bin/env python3


def climb_stairs(n: int) -> int:
def climb_stairs(number_of_steps: int) -> int:
"""
LeetCdoe No.70: Climbing Stairs
Distinct ways to climb a n step staircase where
each time you can either climb 1 or 2 steps.
Distinct ways to climb a number_of_steps staircase where each time you can either
climb 1 or 2 steps.

Args:
n: number of steps of staircase
number_of_steps: number of steps on the staircase

Returns:
Distinct ways to climb a n step staircase
Distinct ways to climb a number_of_steps staircase

Raises:
AssertionError: n not positive integer
AssertionError: number_of_steps not positive integer

>>> climb_stairs(3)
3
Expand All @@ -23,18 +23,17 @@ def climb_stairs(n: int) -> int:
>>> climb_stairs(-7) # doctest: +ELLIPSIS
Traceback (most recent call last):
...
AssertionError: n needs to be positive integer, your input -7
AssertionError: number_of_steps needs to be positive integer, your input -7
"""
assert (
isinstance(n, int) and n > 0
), f"n needs to be positive integer, your input {n}"
if n == 1:
isinstance(number_of_steps, int) and number_of_steps > 0
), f"number_of_steps needs to be positive integer, your input {number_of_steps}"
if number_of_steps == 1:
return 1
dp = [0] * (n + 1)
dp[0], dp[1] = (1, 1)
for i in range(2, n + 1):
dp[i] = dp[i - 1] + dp[i - 2]
return dp[n]
previous, current = 1, 1
for _ in range(number_of_steps - 1):
current, previous = current + previous, current
return current


if __name__ == "__main__":
Expand Down