Count

Climbing Stairs

• Time: O(n)
• Space: O(n)

public int climbStairs(int n) {
    if (n < 3) {
        return n;
    }
    // f[i] = f[i-1] + f[i-2];
    int[] dp = new int[n + 1];
    dp[1] = 1;
    dp[2] = 2;
    for (int i = 3; i <= n; i++) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    return dp[n];
}