70. Climbing Stairs

题目 https://leetcode.com/problems/climbing-stairs/description/

if n <= 1:
            return 1
        if n == 2:
            return 2
        if n > 2:
            return Solution().climbStairs(n-1) +Solution().climbStairs(n-2)

class Solution:
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        n_1, n_2 = 1, 2
        i, j = 1, 1
        if n == 1:
            i = 0
        if n == 2:
            j = 0
        while ( n > 3):
            # flag = j
            # j = i
            # i = i + flag
            i = i + j
            j = i - j
            n-=1;
        print(i,j,n)
        return i * n_2 + j * n_1

def climbStairs(self, n):
    a = b = 1
    for _ in range(n):
        a, b = b, a + b
    return a

int climbStairs(int n) {
    int a = 1, b = 1;
    while (n--)
        a = (b += a) - a;
    return a;
}