폭력의 귀속과 동태적 기획

public class Factorial {
    public static int factorial(int num) {
        if (num == 1) {
            return 1;
        }
        return factorial(num - 1) * num;
    }

    public static void main(String[] args) {
        System.out.println(factorial(3));
    }
}

/**
 *      
 */
public class Hanoi {
    public static void hanoi(int N, String from, String to, String help) {
        if (N == 1) {
            System.out.println("move 1 from" + from + "to" + to);
        } else {
            hanoi(N-1,from,help,to);
            System.out.println("move"+ N +"from"+from+"to"+to);
            hanoi(N-1,help,to,from);
        }
    }


    public static void main(String[] args) {
        hanoi(3," "," "," ");
    }
}

public class PrintAllSubsquences {

    /**
     *              ，      
     * @param str
     */
    public static void printAllSubsquences(String str) {
        char[] chars = str.toCharArray();
        process(chars,0,"");
    }

    public static void process(char[] chars,int i,String res) {
        if (i == chars.length) {
            System.out.println(res);
            return;
        }
        process(chars,i+1,res);
        process(chars,i+1,res+chars[i]);
    }


    public static void main(String[] args) {
        String test = "abc";
        printAllSubsquences(test);
    }
}

/**
 *          ，                  
 *   ，     。 N  ，     。
 */

public class Cow {
    public static int cowNum(int year) {
        if (year < 0) {
            return 0;
        }
        if (year == 1 || year == 2 || year == 3) {
            return year;
        } else {
            return  cowNum(year - 1) + cowNum(year - 3);
        }

    }


    public static void main(String[] args) {
        System.out.println(cowNum(20));
    }
}

public class IsSum {

    public static boolean isSum(int[] arr,int sum, int aim,int i) {
        if (i==arr.length) {
            return sum==aim;
        }
        return isSum(arr, sum, aim, i + 1) || isSum(arr,sum+arr[i],aim,i+1);
    }

    public static void main(String[] args) {
        int[] arr = { 1, 4, 8 };
        int aim = 5;
        System.out.println(isSum(arr, 0,aim,0));

    }
}