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

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