Add HW01 exercises

HW01/EvenSum_04.java

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+import java.util.ArrayList;
+public class EvenSum {
+
+    public static int sumEvenIndices(int[] array) {
+        ArrayList<Integer> list = new ArrayList<>();
+
+        for (int n : array) {
+            list.add(n);
+        }
+
+        int sum = 0;
+        for (int i = 0; i < list.size(); i++) {
+            if (i % 2 == 0) {
+                sum += list.get(i);
+            }
+        }
+        return sum;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = {4, 7, 2, 9, 5};
+        System.out.println("Sum = " + sumEvenIndices(nums));
+    }
+}

HW01/Factorial_02.java

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+import java.util.Scanner;
+public class Factorial{
+    public static void main(String[] args){
+        Scanner num = new Scanner(System.in);
+        long n = num.nextInt();
+        long result = 1;
+
+        for (int i=1 ; i <= n; i++){
+            result *= i;
+        }
+        System.out.println(n + "! = " + result);
+    }
+}

HW01/HelloWorld_01.java

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+public class HelloWorld {
+    public static void main(String[] args) {
+        System.out.println("Hello, World!");
+    }
+}

HW01/Palindrome_03.java

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+import java.util.Scanner;
+public class Palindrome {
+    static boolean isPalin(String s){
+        int i = 0;
+        int j = s.length()-1;
+
+        while (i < j) {
+            if (s.charAt(i) != s.charAt(j)){
+                return false;
+            }
+            i++;
+            j--;
+        }
+
+        return true;
+    }
+    public static void main(String[] args){
+
+    Scanner sc = new Scanner(System.in);
+    String str = sc.nextLine();
+
+    boolean isPal = isPalin(str);
+    System.out.println("is "+ str+ " palindrome? "+ isPal);
+
+    }
+}

HW01/PrimeFactors_05.java

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+import java.util.Scanner;
+import java.util.ArrayList;
+
+public class PrimeFactors {
+    public static ArrayList<Integer> Factors(int num){
+        ArrayList<Integer>  factors = new ArrayList<>();
+
+        if (num <= 1){
+            System.out.println("no prime factor!.");
+        }
+
+        while (num%2 == 0){
+            factors.add(2);
+            num /= 2;
+        }
+        for(int i = 3; i*i <= num; i+=2){
+            while (num%i == 0){
+                factors.add(i);
+                num /= i;
+            }
+        }
+        if (num > 1 ){
+            factors.add(num);
+        }
+        return factors;
+    }
+    public static void main(String[] args){
+        Scanner sc = new Scanner(System.in);
+        int number = sc.nextInt();
+        ArrayList<Integer> factors = Factors(number);
+         if (!factors.isEmpty()){
+             System.out.println("factors =  "+ factors);
+         }
+    }
+}