LeetCode(70)题解: climbing-stairs

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

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?

1)递归： 超时

class Solution {
public:
int climbStairs(int n) {
if (n==1)
return 1;
if(n==2)
return 2;
return climbStairs(n-1)+climbStairs(n-2);
}
};

2）非递归， 避免嵌套调用

递推公式

a_n=a_{n-1}+a_{n-2}.

a_1=1, a_2=2.

问题：给定n求a_n。其实就是斐波那契数列。

AC代码：

class Solution {
public:
int climbStairs(int n) {
if (n==1)
return 1;
if (n==2)
return 2;
int t=2,x=1,y=2,z;
while(t!=n){
t++;
z=x+y;
x=y;
y=z;
}
return z;
}
};