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:

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;
}
};