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==)
            return ;
        if(n==)
            return ;
        return climbStairs(n-)+climbStairs(n-);
    }
};

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==)
             return ;
         if (n==)
             return ;
         int t=,x=,y=,z;
         while(t!=n){
             t++;
             z=x+y;
             x=y;
             y=z;
         }
         return z;
     }
 };