Exercise file

Exercises.java

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+import java.util.Scanner;
+
+public class Exercises {
+
+    /*
+        complete this function to check if the input number is prime or not
+     */
+    public boolean isPrime(long n) {
+        // todo
+        if (n <= 1) return false;
+        for (int i = 2; i <= n / 2; i++) {
+            if (n % i == 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /*
+        implement an algorithm to find out the index of input number in a fibonacci sequence starting from 0, 1
+        e.g. 0, 1, 1, 2, 3, 5, ...
+        indices start from 0, e.g. 3 is the index 4 of this sequence
+        if the input is not a fibonacci number with description above, return -1
+     */
+    public long fibonacciIndex(long n) {
+        // todo
+        long a = 0, b = 1, index = 1;
+        while (b < n) {
+            long temp = a + b;
+            a = b;
+            b = temp;
+            index++;
+        }
+        if (b == n) {
+            return index;
+        }
+        return -1;
+    }
+
+    /*
+        you should create a triangle with "*" and return a two-dimensional array of characters based on that
+        the triangle's area is empty, which means some characters should be " "
+
+        example 1, input = 3:
+        *
+        **
+        ***
+
+        example 2, input = 5:
+        *
+        **
+        * *
+        *  *
+        *****
+
+        the output has to be a two-dimensional array of characters, so don't just print the triangle!
+     */
+    public char[][] generateTriangle(int n) {
+        // todo
+        char[][] triangle = new char[n][];
+
+        for (int i = 0; i < n; i++) {
+            triangle[i] = new char[i + 1];
+            for (int j = 0; j <= i; j++) {
+                if (i == n - 1 || j == 0 || j == i) {
+                    triangle[i][j] ='*' ;
+                }else {
+                    triangle[i][j] = ' ';
+                }
+            }
+        }
+        return triangle;
+    }
+
+    public static void main(String[] args) {
+        // you can test your code here, but then it should be checked with test cases
+        Scanner in = new Scanner(System.in);
+
+        System.out.print("Enter a number to check if it's prime: ");
+        long a = in.nextLong();
+        Exercises p = new Exercises();
+        boolean result = p.isPrime(a);
+        System.out.println("Is the number prime? " + result);
+
+        System.out.print("Enter a number to find its Fibonacci index: ");
+        long b = in.nextLong();
+        long fibonacciIndex = p.fibonacciIndex(b);
+        System.out.println("Fibonacci index of " + b + " is: " + fibonacciIndex);
+
+        System.out.print("Enter the size for the triangle: ");
+        int c = in.nextInt();
+        char[][] triangle = p.generateTriangle(c);
+
+        System.out.println("Triangle:");
+        for (int i = 0; i < triangle.length; i++) {
+            for (int j = 0; j < triangle[i].length; j++) {
+                System.out.print(triangle[i][j]);
+            }
+            System.out.println();
+        }
+    }
+}