0. 题目
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.
Example 1:
Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
方式1. 1 step + 1 step
方式2. 2 steps
Example 2:
Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
方式1. 1 step + 1 step + 1 step
方式2. 1 step + 2 steps
方式3. 2 steps + 1 step
1. c++版本
int climbStairs(int n) {
if ( n==1 || n==2)
return n;
return climbStairs(n-1) + climbStairs(n-2);
}
直接递归，会出现栈溢出
int climbStairs(int n) {
if (n == 1 || n == 2)
return n;
double f1 = 1, f2 = 2, tmp;
while (n > 2) {
tmp = f1;
f1 = f2;
f2 = tmp + f1;
n--;
}
return f2;
}
2.python版本
def climbStairs(self, n):
"""
:type n: int
:rtype: int
"""
if n == 1 or n == 2:
return n
f1, f2 = 1, 2
while n > 2:
tmp = f1
f1 = f2
f2 = f1 + tmp
n = n - 1
return f2
