Algorithm-day04

Algorithm/day04/BinaryNum.java

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+package day04;
+
+import java.util.Scanner;
+//10진수 정수값을 넘기면 2진수 문자열로 출력하는 함수를 재귀함수로 구현해보세요
+public class BinaryNum {
+
+	public static void binaryNum(int num) {
+		if(num<=0) return;
+		binaryNum(num/2);
+		System.out.print(num%2);
+	}//----------------------------------
+
+	public static void radixNum(int num, int radix) {
+		if(num<=0) return;
+		radixNum(num/radix, radix);
+		int mod=num%radix;
+		String str="0123456789ABCDEF";
+		System.out.print(str.charAt(mod));
+	}//--------------------------------
+
+	public static void main(String[] args) {
+		Scanner sc = new Scanner(System.in);
+		System.out.println("정수를 입력하세요=>");
+		int num = sc.nextInt();
+		binaryNum(num);
+		System.out.println();
+
+		System.out.println(num+"의 8진수 값: ");
+		radixNum(num, 8);
+		System.out.println();
+
+		System.out.println(num+"의 16진수 값: ");
+		radixNum(num, 16);
+		System.out.println();
+	}
+
+}

Algorithm/day04/Emp.java

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+package day04;
+//Comparator인터페이스를 상속받는 클래스를 inner class로 만들자
+import java.util.*;
+public class Emp {
+	private String name;//이름
+	private int height;//키
+	public Emp() {
+
+	}
+	public Emp(String n, int h) {
+		name=n;
+		height=h;
+	}
+	public String toString() {
+		return "["+name+" : "+height+"cm]";
+	}
+	public static final Comparator<Emp> HEIGHT_ORDER=new HeightOrderComparator();
+	//키 오름차순 정렬을 위한 Comparator클래스를 만들고 해당 객체를 생성하자
+	static class HeightOrderComparator implements Comparator<Emp>{
+		@Override
+		public int compare(Emp e1, Emp e2) {
+			/*if(e1.height==e2.height) return 0;
+			else if(e1.height>e2.height) return 1;
+			else return -1;*/
+//			return e1.height-e2.height; //오름차순
+			return e2.height-e1.height; //내림차순
+		}
+	}////////////////
+
+	//이름 오름차순 정렬을 위한 Comparator
+	public static final Comparator<Emp> NAME_ORDER=new NameOrderComparator();
+
+	static class NameOrderComparator implements Comparator<Emp>{
+		public int compare(Emp e1, Emp e2) {
+			return e1.name.compareTo(e2.name);
+		}
+	}
+
+
+}//////////////////////

Algorithm/day04/Factorial.java

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+package day04;
+/*n!
+1! : 1
+2! : (1)x 2
+3! : (1x2)x3
+4! : (1x2x3)x4
+5! : (1x2x3x4)x5
+n! : (n-1)!xn
+여기서 1!=1 그리고 n!=nx(n-1)! 라는 팩토리얼 성질을 이용해서 프로그램을 만들어보자
+*/
+import java.util.*;
+public class Factorial {
+
+	public static int factorial(int num) {
+		if(num==1) return 1;
+		String str=(num==1)?"=":"x";
+		System.out.print(num+str);
+		return factorial(num-1);
+	}
+
+	public static void main(String[] args) {
+		Scanner sc = new Scanner(System.in);
+		System.out.println("정수를 입력하세요=>");
+		int num = sc.nextInt();
+		System.out.println(factorial(num));
+	}
+
+}

Algorithm/day04/Fibonacci.java

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+package day04;
+
+import java.util.Scanner;
+
+public class Fibonacci {
+// 1 1 2 3 5 8 13 
+	public static void fibo(int n) {//n은 항
+		int num1=1;
+		int num2=1;
+		int num3=0;
+		System.out.println(num1+" "+num2);
+		for(int i=0; i<n-2; i++) {
+			num3=num1+num2;
+			System.out.println(num3+" ");
+			num1=num2;
+			num2=num3;
+		}
+	}
+	//피보나치 수열을 재귀함수를 이용해서 구현하기
+	public static int fibo2(int n) {
+		if(n==1) return 1;
+		if(n==2) return 1;
+		return fibo2(n-2)+fibo2(n-1);
+		//n번째 항의 앞과 앞의 앞을 더해 반환
+	}//-----------------------------------------
+
+	static int [] arr;
+	public static int fibo3(int n) {
+		if(n==1) return arr[n]=1;
+		else if(n==2) return arr[n]=1;
+		else return arr[n]=fibo3(n-2)+fibo3(n-1);
+	}
+
+	public static void main(String[] args) {
+		Scanner sc = new Scanner(System.in);
+		System.out.println("정수 입력: ");
+		int n= sc.nextInt();
+//		fibo(n);
+		for(int i=1; i<=n; i++) {
+		System.out.print(fibo2(i)+", ");
+		}
+		System.out.println("\n------------------");
+		arr=new int[n+1];
+		fibo3(n);
+
+		for(int a: arr) {
+			if(a==0) continue;
+			System.out.print(a+", ");
+		}
+	}
+
+}

Algorithm/day04/MyArrayList.java

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+package day04;
+
+public class MyArrayList<E> {
+
+	private Object[]data;
+	private int capacity;
+	private int index;
+
+	public MyArrayList() {
+		this(5);
+	}
+
+	public MyArrayList(int initCapa) {
+		this.capacity=initCapa;
+		this.data=new Object[capacity];
+		this.index=0;
+
+	}
+	//데이터 추가
+	public void add(E obj) {
+		if(index>=capacity-1) {//데이터가 꽉 찼다면 => 두배로 증가시키자
+			doubling();
+		}
+		data[index++]=obj;
+	}//---------------------
+	private void doubling() { 
+		this.capacity= this.capacity*2;//2배로
+		Object []newData=new Object[this.capacity];
+		//기존 배열에 저장된 데이터를 새로운 배열로 옮기자
+		for(int i=0; i<data.length; i++) {
+			newData[i]=data[i];
+		}
+		this.data=newData;
+		//멤버변수data에 새로운 배열의 주소값을 전달한다
+		System.out.printf("index: %d, capacity: %d, size: %d%n",index, capacity, this.size());
+	}//----------------------------------------
+	//리스트에 담긴 데이터 개수를 반환
+	public int size() {
+		return index;
+	}//----------------------------
+	//데이터 꺼내기
+	public E get(int i){
+		if(i>index-1) {
+			throw new ArrayIndexOutOfBoundsException();
+		}else if(i<0) {
+			throw new RuntimeException("Negative Index Value");
+		}
+		Object val=data[i];
+		return (E)val;
+	}//----------------------------
+	//특정 인덱스의 데이터 삭제
+	public void remove(int i) {
+		if(i>index-1) {
+			throw new ArrayIndexOutOfBoundsException();
+		}else if(i<0) {
+			throw new RuntimeException("Negative Index Value");
+		}
+		for(int k=i; k<this.data.length-1; k++) {
+			data[k]=data[k+1]; //뒤에 있는 요소를 옆으로 이동시킨다
+		}
+		this.index--;
+	}
+
+}//////////////////////////////////////////////////////////
+
+
+

Algorithm/day04/MyArrayListTest.java

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+package day04;
+
+public class MyArrayListTest {
+
+	public static void main(String[] args) {
+		//MyArrayList를 생성해서
+		//정수형 객체를 몇개 저장한 후에 반복문 이용해서 한꺼번에 출력하기
+
+		MyArrayList<Integer> arr = new MyArrayList();//초기용량 5
+		arr.add(10);
+		arr.add(20);
+		arr.add(30);
+		arr.add(40);
+		System.out.println("arr.size(): "+arr.size());
+		arr.add(50);
+		arr.add(60);
+		System.out.println("arr.size(): "+arr.size());
+
+		for(int i=0; i<arr.size(); i++) {
+			Integer ival = arr.get(i);
+			System.out.println(ival);
+		}
+//		arr.remove(7);
+		arr.remove(1);
+		System.out.println("--삭제후-----------------------");
+		for(int i=0; i<arr.size(); i++) {
+			Integer ival=arr.get(i);
+			System.out.println(ival);
+		}
+
+		MyArrayList<String> arr2 = new MyArrayList<>();
+
+		arr2.add("Hello");
+		arr2.add("Hi");
+
+		String str=arr2.get(1);
+		System.out.println(str);
+
+
+	}
+
+}