斐波那契数

class Solution {
    public int fib(int n) {
        if (n < 2)
            return n;

        int p = 0, q = 0, ans = 1;
        //滑动数组
        for (int i = 2; i <= n; i ++) {
            p = q;
            q = ans;
            ans = p + q;
        }
        return ans;
    }
}