JkB collection framwork

src/main/java/Collections/Practice/CollectionBasics.java

@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
 
 public class CollectionBasics {
     public static void main(String[] args) {
@@ -27,9 +28,11 @@ public static void main(String[] args) {
      Return the sum of all numbers in the collection
     */
     public static int sum(Collection<Integer> numbers) {
-
         int total = 0;
 
+        for (int num : numbers) {
+            total += num;
+        }
         // TODO:
         // Loop through the collection
         // Add each number to total
@@ -43,9 +46,13 @@ public static int sum(Collection<Integer> numbers) {
      Count how many numbers are even
     */
     public static int countEven(Collection<Integer> numbers) {
-
         int count = 0;
 
+        for (int num : numbers) {
+            if (num % 2 == 0) {
+                count++;
+            }
+        }
         // TODO:
         // Loop through the collection
         // If the number is even, increase count
@@ -59,9 +66,13 @@ public static int countEven(Collection<Integer> numbers) {
      Find the largest number in the collection
     */
     public static int findMax(Collection<Integer> numbers) {
-
         int max = Integer.MIN_VALUE;
 
+        for (int num : numbers) {
+            if (num > max) {
+                max = num;
+            }
+        }
         // TODO:
         // Loop through numbers
         // Update max if current number is larger
@@ -90,9 +101,14 @@ public static boolean hasDuplicates(Collection<Integer> numbers) {
      Count how many times a target value appears
     */
     public static int countOccurrences(Collection<Integer> numbers, int target) {
-
         int count = 0;
 
+        for (int num : numbers) {
+            if (num == target) {
+                count++;
+            }
+        }
+
         // TODO:
         // Loop through numbers
         // If number equals target, increase count
@@ -107,9 +123,14 @@ public static int countOccurrences(Collection<Integer> numbers, int target) {
      that only contains numbers greater than 20
     */
     public static Collection<Integer> filterGreaterThanTwenty(Collection<Integer> numbers) {
-
         Collection<Integer> result = new ArrayList<>();
 
+        for (int num : numbers) {
+            if (num > 20) {
+                result.add(num);
+            }
+        }
+
         // TODO:
         // Loop through numbers
         // Add numbers greater than 20 to result

src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java

@@ -1,11 +1,10 @@
 package CollectionsHackerrank;
 
-import java.util.List;
-import java.util.Map;
-import java.util.Queue;
+import java.util.*;
+
 
 public class CollectionsHackerrankProblems {
-    public class CollectionsHackerrankPractice {
+
 
         public static void main(String[] args) {
 
@@ -21,11 +20,17 @@ public static void main(String[] args) {
         Input: [1,2,2,3,4,4,5]
         Output: [1,2,3,4,5]
         */
-        public static List<Integer> removeDuplicates(List<Integer> numbers) {
 
+
+
+        public static List<Integer> removeDuplicates(List<Integer> numbers) {
+            Set<Integer> set = new LinkedHashSet<>(numbers);//Have to convert List to Set
+            //Set removes duplicates *LinkedHashSet Keeps the value in order
+            return new ArrayList<>(set);//Covert the Set back to List
+            // because the method calls for a List *Set is just for removing Duplicates
             // TODO: Implement this method
 
-            return null;
+
         }
 
         /*
@@ -37,10 +42,20 @@ public static List<Integer> removeDuplicates(List<Integer> numbers) {
         Output: {1=1, 2=2, 3=3}
         */
         public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
-
+            //takes a list of numbers
+            //returns a map of counts
+            Map<Integer, Integer> map = new HashMap<>();//This creates an empty HashMap called map
+            for (int num : numbers) { //for each loop to run through the list
+                map.put(num, map.getOrDefault(num, 0) + 1);
+                //This line basically updates the counter for the number
+                //it Gets the value for this key
+                // and If the key does not exist, return 0
+            }
+
+            return map;//returns the final results
             // TODO: Implement this method
 
-            return null;
+
         }
 
         /*
@@ -52,10 +67,21 @@ public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
         Output: 5
         */
         public static Integer firstUnique(List<Integer> numbers) {
+            //THe method header
+            Map<Integer, Integer> map = countFrequency(numbers);//calling
 
-            // TODO: Implement this method
+            for (int num : numbers) {
+                if (map.get(num) == 1) {
+                    //get the count for this number
+                    return num;
+                    //returning the number that appears once
+                }
+            }
 
             return null;
+            // TODO: Implement this method
+
+
         }
 
         /*
@@ -69,10 +95,21 @@ public static Integer firstUnique(List<Integer> numbers) {
         Output: true
         */
         public static boolean twoSum(List<Integer> numbers, int target) {
+            Set<Integer> seen = new HashSet<>();
+            //This set stores numbers we have already seen.
 
-            // TODO: Implement this method
+            for (int num : numbers) {
+                if (seen.contains(target - num)) {
+                    //if we already saw the number that would complete the target.
+                    return true;
+                }
+                seen.add(num);//adds the number into the seen object that was created
+            }
 
             return false;
+            // TODO: Implement this method
+
+
         }
 
         /*
@@ -84,10 +121,11 @@ public static boolean twoSum(List<Integer> numbers, int target) {
         Output: 3
         */
         public static int countUniqueWords(List<String> words) {
-
+            Set<String> set = new HashSet<>(words);
+            return set.size();
             // TODO: Implement this method
 
-            return 0;
+
         }
 
         /*
@@ -100,9 +138,27 @@ public static int countUniqueWords(List<String> words) {
         */
         public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
 
+            // Create a stack to help reverse the order
+            // Stacks are LIFO (Last In First Out)
+            Stack<Integer> stack = new Stack<>();
+
+            // Move all elements from the queue into the stack
+            // Queue removes from the front using poll()
+            while (!queue.isEmpty()) {
+                stack.push(queue.poll()); // remove from queue and push into stack
+            }
+
+            // Now move everything back from the stack into the queue
+            // Since stacks remove the last element added, the order becomes reversed
+            while (!stack.isEmpty()) {
+                queue.offer(stack.pop()); // pop from stack and add back to queue
+            }
+
+            // Return the reversed queue
+            return queue;
             // TODO: Implement this method
 
-            return null;
+
         }
 
         /*
@@ -118,9 +174,37 @@ public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
         */
         public static boolean isBalanced(String expression) {
 
+            // Create a stack to keep track of opening parentheses
+            Stack<Character> stack = new Stack<>();
+
+            // Loop through each character in the string
+            for (char c : expression.toCharArray()) {
+
+                // If we see an opening parenthesis, push it onto the stack
+                if (c == '(') {
+                    stack.push(c);
+                }
+
+                // If we see a closing parenthesis
+                else if (c == ')') {
+
+                    // If the stack is empty, there was no matching '('
+                    // Example: ")("
+                    if (stack.isEmpty()) {
+                        return false;
+                    }
+
+                    // Otherwise remove the matching '(' from the stack
+                    stack.pop();
+                }
+            }
+
+            // If the stack is empty, all parentheses matched correctly
+            // If not empty, there are extra '(' left
+            return stack.isEmpty();
             // TODO: Implement this method
 
-            return false;
+
         }
 
         /*
@@ -133,9 +217,35 @@ public static boolean isBalanced(String expression) {
         */
         public static Integer mostFrequent(List<Integer> numbers) {
 
+            // Count how many times each number appears
+
+            Map<Integer, Integer> map = countFrequency(numbers);
+
+            // Track the highest frequency seen so far
+            int max = 0;
+
+            //  Track which number has that highest frequency
+            Integer result = null;
+
+            // Loop through each number in the map
+            for (int key : map.keySet()) {
+
+                // If this number occurs more times than the current max
+                if (map.get(key) > max) {
+
+                    // Update max frequency
+                    max = map.get(key);
+
+                    // Update the number that has the highest frequency
+                    result = key;
+                }
+            }
+
+            // Return the number that appears most frequently
+            return result;
             // TODO: Implement this method
 
-            return null;
+
         }
 
         /*
@@ -153,9 +263,32 @@ public static Integer mostFrequent(List<Integer> numbers) {
         */
         public static Map<Integer, List<String>> groupByLength(List<String> words) {
 
+            // Create a map where:
+            // key = length of a word
+            // value = list of words with that length
+            Map<Integer, List<String>> map = new HashMap<>();
+
+            // Loop through each word in the input list
+            for (String word : words) {
+
+                // Find the length of the current word
+                int length = word.length();
+
+                //  If this length is not already a key in the map
+                // create a new list for this length
+                if (!map.containsKey(length)) {
+                    map.put(length, new ArrayList<>());
+                }
+
+                //  Add the word to the list for its length
+                map.get(length).add(word);
+            }
+
+            //  Return the map grouping words by their length
+            return map;
             // TODO: Implement this method
 
-            return null;
+
         }
 
         /*
@@ -170,9 +303,31 @@ public static Map<Integer, List<String>> groupByLength(List<String> words) {
         */
         public static int maxSlidingWindowSum(List<Integer> numbers, int k) {
 
+            // Initialize a variable to keep track of the maximum sum
+            int maxSum = 0;
+
+            // Loops over each possible starting index of a window of size k
+            for (int i = 0; i <= numbers.size() - k; i++) {
+
+                // Initialize sum for the current window
+                int currentSum = 0;
+
+                //Sum up all numbers in the current window
+                for (int j = i; j < i + k; j++) {
+                    currentSum += numbers.get(j);
+                }
+
+                // Update maxSum if the current window sum is bigger
+                if (currentSum > maxSum) {
+                    maxSum = currentSum;
+                }
+            }
+
+            // Returns the largest sum found among all windows
+            return maxSum;
             // TODO: Implement this method
 
-            return 0;
+
         }
     }
-}
+