Java / Programs
1.
Write a Java program to find the last repeating character in a String.
2.
Write a Java program to find the first repeating character in a String.
3.
Write a simple Java program to find the sum of all integers in a List.
4.
Write a Java program to find the subArray in an Integer Array that has maximum Sum of the elements.
5.
Java program to find the first non-repeating character in a String.
6.
Java program to find the last non-repeating character in a String.
7.
Write a Java program to calculate Fibonacci of N using memoize recursive method.
8.
Write a Java program to count negative numbers in a 2-dimensional array which is sorted row and column wise. (Amazon interview question)
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1. Write a Java program to find the last repeating character in a String.
The below program is implemented using Java 8.
public class LastOccuranceOfRepeatingChar { public static void main(String[] args) { String str = "abcdklja"; Set<Integer> myTempHashSet = new HashSet<>(); str.codePoints().filter(i -> myTempHashSet.add(i) == false).reduce((first, second) -> second) .ifPresent(c -> System.out.println("Last repeating char: " + (char) c)); } }
The below version is for Java 7 or less.
public class LastOccuranceOfRepeatingCharJava7 { public static void main(String[] args) { String str = "abcdklja"; Set<Character> myTempHashSet = new HashSet<>(); char lastChar = 0; for (int i = 0; i < str.length(); i++) { if (myTempHashSet.add(str.charAt(i)) == false) { lastChar = str.charAt(i); } } System.out.println("Last repeating char: " + lastChar); } }
2. Write a Java program to find the first repeating character in a String.
The below program is implemented using Java 8.
public class FirstRepeatingChar { public static void main(String[] args) { String str = "abcdklha"; Set<Integer> myTempHashSet = new HashSet<>(); str.codePoints().filter(i -> myTempHashSet.add(i) == false).findFirst() .ifPresent(i -> System.out.println("First repeating Char: " + (char) i)); } }
Java7 version.
public class FirstRepeatingCharJava7 { public static void main(String[] args) { String str = "abcdklha"; Set<Character> myTempHashSet = new HashSet<>(); for (int i = 0; i < str.length(); i++) { if (myTempHashSet.add(str.charAt(i)) == false) { System.out.println("First repeating character: " + str.charAt(i)); break; } } } }
3. Write a simple Java program to find the sum of all integers in a List.
public class SumofIntegersOfList { public static void main(String[] args) { List<Integer> myList = Arrays.asList(1, 2, 3, 4, 5); System.out.println("Sum :" + myList.stream().reduce((i, j) -> i + j)); } }
4. Write a Java program to find the subArray in an Integer Array that has maximum Sum of the elements.
public class FindSubArrayWithMaxSum { public static void main(String[] args) { // Creating a bucket of integer array with various test values for unit testing int[][] myArr = { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 10, -11 }, { 1, 2, 3, 0, 4, 3, -1, 3, 5, 5, 6, 6, -2, 50 }, { -3, 0, -1 }, { 0, -1 }, {}, { -2 }, { 2 }, { 0 }, { 1, 2, 3, -1, 1, 2, 3, 4, 0, -1, 1, 1 } }; // For each of the above data set find the sumArray with Maximum sum IntStream.range(0, myArr.length).mapToObj(i -> myArr[i]).parallel() .forEach(FindSubArrayWithMaxSum::findMaxSumSubArray); } static void findMaxSumSubArray(int[] myArr) { if (myArr.length == 0) return; int positionI = 0, positionJ = 0; int tempPositionI = 0, tempPositionJ = 0; int maxSum, tempSum; maxSum = tempSum = myArr[0]; for (int i = 1; i < myArr.length; i++) { if (tempPositionI >= i || tempSum < 0) { tempPositionI = tempPositionJ = i; tempSum = myArr[i]; continue; } if ((tempSum + myArr[i]) >= tempSum) { tempSum += myArr[i]; tempPositionJ = i; } else if (i + 1 < myArr.length) { positionI = tempPositionI; positionJ = tempPositionJ; maxSum = tempSum; tempPositionI = i + 1; } } if (tempSum > maxSum) { positionI = tempPositionI; positionJ = tempPositionJ; maxSum = tempSum; } System.out.println( Arrays.toString(myArr) + " >> Start Position: " + positionI + " End Position: " + positionJ + ", Sum: " + maxSum); } }
5. Java program to find the first non-repeating character in a String.
public class FirstNonRepeatingChar { public static void main(String[] args) { String str = "abccak"; HashMap<Character,Boolean> myLinkedMap = new LinkedHashMap<>(); for (int i=0; i<str.length(); i++) { char c = str.charAt(i); if (myLinkedMap.containsKey(c)) { myLinkedMap.put(c, false); } else { myLinkedMap.put(c,true); } } System.out.println ("First non-repeating char: " + myLinkedMap.entrySet().stream().filter(map ->map.getValue() == true).findFirst().map (p -> p.getKey())); } }
6. Java program to find the last non-repeating character in a String.
public class LastNonRepeatingChar { public static void main(String[] args) { String str = "abccak"; HashMap<Character,Boolean> myLinkedMap = new LinkedHashMap<>(); for (int i=0; i<str.length(); i++) { char c = str.charAt(i); if (myLinkedMap.containsKey(c)) { myLinkedMap.put(c, false); } else { myLinkedMap.put(c,true); } } System.out.println ("Last non-repeating char: " + myLinkedMap.entrySet().stream().filter(map ->map.getValue() == true).reduce((first,second) ->second).map (p -> p.getKey())); } }
7. Write a Java program to calculate Fibonacci of N using memoize recursive method.
public class Fibonacci { static int n; private int[] memoise_array = new int[n]; public static void main(String[] args) { n = 6; System.out.println(new Fibonacci().fibonacci(n)); } int fibonacci(int n) { if (memoise_array[n - 1] != 0) return memoise_array[n - 1]; else if (n == 1 || n == 2) return 1; else memoise_array[n - 1] = fibonacci(n - 1) + fibonacci(n - 2); return memoise_array[n - 1]; } }
8. Write a Java program to count negative numbers in a 2-dimensional array which is sorted row and column wise. (Amazon interview question)
public class CountNegativeNumbers { /* * Amazon interview question */ public static void main(String[] args) { int[][] matrix = new int[][] { { -3, -2, -1, 0 }, { -2, -1, 0, 1 }, { -1, 0, 1, 2 }, { -1, 1, 2, 3 } }; int count = 0; int k = matrix[0].length - 1; for (int i = 0; i < matrix.length; i++) { for (int j = k; j >= 0; j--) { if (matrix[i][j] < 0) { count = count + j + 1; k = j; break; } } } System.out.println("Total negative nos: " + count); } }
