Question

what is the time complexity of those ?

//TODO - Question 18
   public static int[][] fillRandomArray4(int n) {
       int[][] arr = new int[n][n];
       for(int i = 0; i < arr.length; i++) {
           arr[i] = new int[] {(int)(Math.random() * 101),
                   (int)(Math.random() * 101),
                   (int)(Math.random() * 101)};
       }
       return arr;
   }
  
  
   //TODO - Question 19
   public static int factorial(int n) {
       if(n == 1 || n == 0) {
           return 1;
       }
       return n * factorial(n-1);
   }
  
  
   //TODO - Question 20 - assume str.length() == n
   public static boolean isPalindrome(String str) {
       if(str.length() == 0 || str.length() == 1) {
           return true;
       }
       if(str.charAt(0) != str.charAt(str.length()-1)) {
           return false;
       } else {
           return isPalindrome(str.substring(1,str.length()-1));
       }
   }

Answer 1

thanks for the questions.

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Question 18

In this method, we are running a for loop n times which is passed to this method as an argument,
there is only 1 for loop without any inner loops, hence the code inside the for loop will run
n times (arr.length will return n)

So the time complexity will be linear and of order O(n)

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Question 19

The method finds the factorial of a number, the function recursively calls itself until the value of n
is 1 or 0, in every call the value of n is decremented by 1, so the number of method call will be equal
to the value of n.

So the time complexity will be linear and of order O(n)

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Question 20

The method finds if a string is palindrome, in every recursive call the length of the string is reduced by 2
that is the first character and last character are removed and the substring is passed as an argument in the
next recursive call.

The total iterations will be for a string of length n is n/2.

So the time complexity will be linear and of order O(n/2) or simply O(n)

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