Requirements gathering
Analysis
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A trivial coding example (i.e. a Calculator) tackled using the following programming paradigms in Java not only to perform well in coding interviews, but also to learn these programming paradigms.
Approach 1: Procedural Programming
Approaches 2 – 4: Object Oriented Programming
Approach 5: Functional Programming (Java 8)
Approach 1: Procedural
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public interface Calculate { abstract int calculate(int operand1, int oerand2, Operator operator); } |
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public enum Operator { ADD, SUBTRACT, DIVIDE, MULTIPLY; } |
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public class CalculateImpl implements Calculate { @Override public int calculate(int operand1, int operand2, Operator operator) { switch (operator) { case ADD: return operand1 + operand2; case SUBTRACT: return operand1 - operand2; case MULTIPLY: return operand1 * operand2; case DIVIDE: return operand1 / operand2; } throw new RuntimeException(operator + "is unsupported"); } } |
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public class CalculatorTest { public static void main(String[] args) { Calculate calc = new CalculateImpl(); int result = calc.calculate(5,6,Operator.ADD); result = calc.calculate(result,6,Operator.MULTIPLY); result = calc.calculate(result,1,Operator.SUBTRACT); result = calc.calculate(result,5,Operator.DIVIDE); System.out.println("result=" + result); } } |
Output: result=13
Approach 2: OOP
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public interface MathCommand<E> { abstract E execute(E operand1, E operand2); } |
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public class AddCommand implements MathCommand<Integer>{ @Override public Integer execute(Integer operand1, Integer operand2) { return operand1 + operand2; } } |
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public class SubtractCommand implements MathCommand<Integer>{ @Override public Integer execute(Integer operand1, Integer operand2) { return operand1 - operand2; } } |
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public class MultiplyCommand implements MathCommand<Integer>{ @Override public Integer execute(Integer operand1, Integer operand2) { return operand1 * operand2; } } |
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public class DivideCommand implements MathCommand<Integer>{ @Override public Integer execute(Integer operand1, Integer operand2) { return operand1 / operand2; } } |
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public class CalculatorTest2 { public static void main(String[] args) { MathCommand<Integer> command = new AddCommand(); Integer result = command.execute(5, 6); command = new MultiplyCommand(); result = command.execute(result, 6); command = new SubtractCommand(); result = command.execute(result, 1); command = new DivideCommand(); result = command.execute(result, 5); System.out.println("result=" + result); } } |
When you have more mathematical operations,
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Java coding interview questions are very common in job interviews. Good coding skills are essentials for passing the peer code reviews with flying colours. Here are 17 coding tips with Java examples. Tip #1: If you are asked to write a function or code, … Read more ›...
Q1. Can you write a function to determine the nth Fibonacci number? The Fibonacci numbers under 2000 are : 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597. Where the zeroth number being 0, first number being 1, … Read more...
Complimenting Fibonacci number coding – iterative and recursive approach, we can improve performance by caching. If you run this
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public class RecursiveFibonacci { public int fibonacci(int n) { if (n == 0 || n == 1) return n; System.out.println("evaluating fibonacci(" + n + ")"); return fibonacci(n - 2) + fibonacci(n - 1); } public static void main(String[] args) { int nThfibonacciNo = new RecursiveFibonacci().fibonacci(5); System.out.println(nThfibonacciNo); } } |
Output
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evaluating fibonacci(5) evaluating fibonacci(3) evaluating fibonacci(2) evaluating fibonacci(4) evaluating fibonacci(2) evaluating fibonacci(3) evaluating fibonacci(2) 5 |
and you can see “fibonacci(3)” is repeated 2 times, “fibonacci(2)” is repeated 3 times, and so on. If you pick a larger number like 21, … Read more...
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Firstly, understand the problem, and write down any considerations & assumptions. Next write pseudocode if that helps. Considerations 1) Pre-codnition check for null or empty input. 2) Loop through the input string, and store each “character” as a key in a map with the value being the “character count”. …...
Q. Can you write code to identify missing numbers in a given array of numbers?
Solution 1: Assuming that the given numbers are in order
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public class MissingNumber { public static void main(String[] args) { int numbers[] = { 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18 }; new MissingNumber().findMissingNumbers(numbers, 0, 20); } private void findMissingNumbers(int[] input, int first, int last) { printMissingNumbersFront(input, first); printMissingNumbersInTheMiddle(input, last); printMissingNumbersBack(input, last); } /** * before 2 * @param input * @param first */ private void printMissingNumbersFront(int[] input, int first) { //0 and 1 are less than 2 as per the above input for (int i = first; i < input[0]; i++) { System.out.println(i); } } /** * after 18 * @param input * @param last */ private void printMissingNumbersBack(int[] input, int last) { // 1 + the last element value is 19. 19 to 20 are less than or equal to the last value of 20 for (int i = 1 + input[input.length - 1]; i <= last; i++) { System.out.println(i); } } /** * between 2 and 18 * @param input * @param last */ private void printMissingNumbersInTheMiddle(int[] input, int last) { //for a given index i, index [i-1]+1 should be equal if present. for (int i = 1; i < input.length; i++) { //e.g. for input[1] = 3, j=1+2 //input[2] = 4, j=1+3 //input[3] = 6, j=4+1, Oops 5 is less than 6 so print //input[4] = 7, j=6+1 //if index[i] < index[i-1] + 1, then number index[i-1] + 1 is missing for (int j = 1+input[i-1]; j < input[i]; j++) { System.out.println(j); } } } } |
Output:
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0 1 5 16 17 19 20 |
The above solution assumes that the numbers are in order (i.e.
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Q. Can you write code to output the perfect number between a given range? Definition: A perfect number is a positive integer that is equal to the sum of its proper divisors. The smallest perfect number is 6, which is the sum of 1, … Read more ›...
Q1. Write a program that prints numbers from 1 to 30, but for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”? A1. … Read more ›...
Q1. Can you write Java code to generate random numbers between a given range? A1. E.g. 0 and 9 or 5 to 35, and so on.
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1 |
Random rand = new Random(); |
The “nextInt()” method works from “0” … Read more ›...
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Q1. Can you write a sample code that will count the number of “A”s in a given text “AAA rating“? Show both iterative and recursive approaches?
A1.
Iteration:
A for loop to traverse through each character of the String “AAA rating”,
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