099Climbing Stairs

def climbStairs(n: int) -> int:
    if n <= 2:
        return n
    prev2, prev1 = 1, 2
    for _ in range(3, n + 1):
        prev2, prev1 = prev1, prev2 + prev1
    return prev1

public int climbStairs(int n) {
    if (n <= 2) return n;
    int prev2 = 1, prev1 = 2;
    for (int i = 3; i <= n; i++) {
        int cur = prev1 + prev2;
        prev2 = prev1;
        prev1 = cur;
    }
    return prev1;
}

fun climbStairs(n: Int): Int {
    if (n <= 2) return n
    var prev2 = 1; var prev1 = 2
    for (i in 3..n) {
        val cur = prev1 + prev2
        prev2 = prev1; prev1 = cur
    }
    return prev1
}

int climbStairs(int n) {
    if (n <= 2) return n;
    int p2 = 1, p1 = 2;
    for (int i = 3; i <= n; i++) {
        int cur = p1 + p2;
        p2 = p1; p1 = cur;
    }
    return p1;
}