leetcode: 70. Climbing Stairs

# You are climbing a stair case. It takes n steps to reach to the top.
#
# Each time you can either climb 1 or 2 steps. 
# In how many distinct ways can you climb to the top?
#
# Note: Given n will be a positive integer.

class Solution():
    def climbStairs(self, n):
        pre, cur = 0, 1
        for _ in range(n):
            pre, cur = cur, pre + cur
        return cur

# Time Limit Exceeded
class Solution():
    def climbStairs(self, n):
        if n == 1:
            return 1
        if n == 2:
            return 2
        return self.climbStairs(n - 1) + self.climbStairs(n - 2)


if __name__ == "__main__":
    assert Solution().climbStairs(2) == 2