climbing_stairs.cpp

/*
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?

Note: Given n will be a positive integer.


Example 1:

Input: 2
Output:  2
Explanation:  There are two ways to climb to the top.

1. 1 step + 1 step
2. 2 steps
Example 2:

Input: 3
Output:  3
Explanation:  There are three ways to climb to the top.

1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

*/


class Solution {
public:
    int climbStairs(int n) {
        int cur_count = 0;
        int prev_count = 0;
        for(int i=1;i<=n;i++)
        {
            if(i==1)
                cur_count = 1;
            else if(i==2)
            {
                cur_count = 2;
                prev_count = 1;
            }
            else
            {
                int tmp = cur_count;
                cur_count = cur_count + prev_count;
                prev_count = tmp;
            }
        }
        return cur_count;
    }
};