LeetCode(70)題解: climbing-stairs

標籤：

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

題目：

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)遞迴：  逾時

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）非遞迴， 避免嵌套調用

遞推公式

 a_n=a_{n-1}+a_{n-2}.

 a_1=1, a_2=2.

問題：給定n求a_n。其實就是斐波那契數列。

AC代碼：

 1 class Solution { 2 public: 3     int climbStairs(int n) { 4         if (n==1) 5             return 1; 6         if (n==2) 7             return 2; 8         int t=2,x=1,y=2,z; 9         while(t!=n){10             t++;11             z=x+y;12             x=y;13             y=z;14         }15         return z;16     }17 };

 

LeetCode(70)題解: climbing-stairs