LeetCode - Climbing Stairs

Climbing Stairs

2013.12.22 04:13

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?

Solution:

　　Search for "Fibonacci sequence" and calculate the nth element in the sequence.

　　Time complexity is O(n), space complexity is O(1).

Accepted code:

 1 class Solution {

 2 public:

 3     int climbStairs(int n) {

 4         // Note: The Solution object is instantiated only once and is reused by each test case.

 5         int f1, f2, f3;

 6         

 7         f1 = 0;

 8         f2 = 1;

 9         

10         if(n <= 0){

11             return 0;

12         }

13         

14         for(int i = 0; i < n; ++i){

15             f3 = f1 + f2;

16             f1 = f2;

17             f2 = f3;

18         }

19         

20         return f3;

21     }

22 };