008 -菲波那切数列

菲波那切数列

(1)递归方法实现

//递归实现斐波那契数列
    public static int calculateOne(int num) {
        if(num==0)return 0;
        if(num==1)return 1;
        return calculateOne(num-1)+calculateOne(num-2);
    }

(2)去重递归方法实现

//去重递归的方法实现菲波那切数列
    public static int calculateTwo(int num) {
        int [] array = new int [num+1];
        return getRecurse(num, array);
    }

    public static int getRecurse(int num, int[] array) {
        if(num==0)return 0;
        if(num==1)return 1;
        if(array[num]!=0)return array[num];
        array[num]=getRecurse(num-1,array)+getRecurse(num-2,array);
        return array[num];
    }

(3)双指针方法实现

  //双指针实现菲波那切数列数列的计算
    private static int calculateThree(int num) {
        if(num==0)return 0;
        if(num==1)return 1;
        int low = 0,high=1;
        for(int i = 2;i<=num;i++)
        {
            int sum = low + high;
            low = high;
            high = sum;
        }
        return high;
    }

(4)递推方法实现

 //递推的方法实现菲波那切数列
    public static int calculateFour(int num) {
        int []array = new int [num+1];
        if(num==0)return 0;
        if(num==1)return 1;
        array[0]=0;
        array[1]=1;
        for(int i =2;i<=num;i++)
        {
            array[i]=array[i-1]+array[i-2];
        }
        return array[num];
    }