LeetCode

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:

class Solution {
public:
    int climbStairs(int n) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int f1, f2, f3;
        
        f1 = 0;
        f2 = 1;
        
        if(n <= 0){
            return 0;
        }
        
        for(int i = 0; i < n; ++i){
            f3 = f1 + f2;
            f1 = f2;
            f2 = f3;
        }
        
        return f3;
    }
};