done

AP1403 - WarmUp/src/main/java/Exercises.java

@@ -1,48 +1,64 @@
 public class Exercises {
 
-    /*
-        complete this function to check if the input number is prime or not
-     */
     public boolean isPrime(long n) {
-        // todo
-        return false;
-    }
+        if (n <= 1) {
+            return false;
+        }
+        for (long i = 2; i <= Math.sqrt(n); 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
-        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 " "
+    public long fibonacciIndex(long n) {
+        if (n < 0) return -1;
+        long a = 0, b = 1;
+        long index = 0;
 
-        example 1, input = 3:
-        *
-        **
-        ***
+        while (a < n) {
+            long temp = a;
+            a = b;
+            b = temp + b;
+            index++;
+        }
 
-        example 2, input = 5:
-        *
-        **
-        * *
-        *  *
-        *****
+        return (a == n) ? index : -1;
+    }
 
-        the output has to be a two-dimensional array of characters, so don't just print the triangle!
-     */
     public char[][] generateTriangle(int n) {
-        // todo
-        return null;
+        char[][] triangle = new char[n][n];
+
+        for (int i = 0; i < n; i++) {
+            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
+        Exercises ex = new Exercises();
+
+
+        System.out.println(ex.isPrime(7)); // true
+        System.out.println(ex.isPrime(10)); // false
+
+
+        System.out.println(ex.fibonacciIndex(3)); // 4
+        System.out.println(ex.fibonacciIndex(6)); // -1
+
+
+        char[][] triangle = ex.generateTriangle(5);
+        for (char[] row : triangle) {
+            System.out.println(new String(row));
+        }
     }
 }