TonyKim9401.java

class Solution {
    public int climbStairs(int n) {
        // Time complexity: O(n);
        // Space complexity: O(n);
        int[] dp = new int[n+1];

        if (n >= 1) dp[1] = 1;
        if (n >= 2) dp[2] = 2;

        for (int i = 3; i <= n; i++) {
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
}