g4-04036. GESP-4级-2025-09-单选-第13题 未做

小杨正在爬楼梯，需要 $n$ 阶才能到达楼顶，每次可以爬 $1$ 阶或 $2$ 阶，求小杨有多少种不同的方法可以爬到楼顶，横线上应填写（ ）。

int climbStairs(int n) {
    if (n <= 2) return n;
    int prev2 = 1;
    int prev1 = 2;
    int current = 0;
    for (int i = 3; i <= n; ++i) {
        ____________    // 在此处填入代码

    }
    return current;
}

• A. ```cpp
  prev2 = prev1;
  prev1 = current;
  current = prev1 + prev2;

- **B.** ```cpp
current = prev1 + prev2;
prev2 = prev1;
prev1 = current;

• C. ```cpp
  current = prev1 + prev2;
  prev1 = current;
  prev2 = prev1;

- **D.** ```cpp
prev1 = current;
prev2 = prev1;
current = prev1 + prev2;