70. Climbing Stairs

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

Solution

class Solution {
    public int climbStairs(int n) {
        //f(n) = f(n-1) + f(n-2)
        if (n == 1 || n == 2)   {return n;}
        int[] map = new int[n];
        map[0] = 1;
        map[1] = 2;
        for (int i = 2; i < n; i++){
            map[i] = map[i-1] + map[i-2];
        }
        return map[n-1];
    }
}