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.

Solution: DP

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        pre_climb = 0
        climb = 1
        for _ in xrange(n):
            pre_climb, climb = climb, pre_climb + climb
        return climb