package pqs;


/**
 * 0 1 2 3 4
 * 0 1 1 2 3 5 8 13...
 * 斐波那契数即前两项相加
 */
public class feibonaqishu {

    /**
     * 递归
     * @param n
     * @return
     */
    public static int fib1(int n){
        if (n <= 1) return n;
        return fib1(n-1) + fib1(n-2);
    }

    /**
     * 优化的算法
     * @param n
     * @return
     */
    public static int fib2(int n){
        if (n <= 1) return n;

        int first = 0;
        int second = 1;

         for (int i=0; i < n -1;i++){
             int sum = first + second;
             first = second;
             second = sum;
         }
         return second;
    }

    public static void main(String[] args) {
        System.out.println(fib2(1));
    }
}