Bobby-Complete-Collections-Lab

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

@@ -1,7 +1,6 @@
 package Collections.Practice;
 
-import java.util.ArrayList;
-import java.util.Collection;
+import java.util.*;
 
 public class CollectionBasics {
     public static void main(String[] args) {
@@ -10,6 +9,7 @@ public static void main(String[] args) {
 
         numbers.add(4);
         numbers.add(8);
+       //numbers.add(8);
         numbers.add(15);
         numbers.add(16);
         numbers.add(23);
@@ -33,7 +33,9 @@ public static int sum(Collection<Integer> numbers) {
         // TODO:
         // Loop through the collection
         // Add each number to total
-
+for(Integer sum: numbers){
+    total += sum;
+}
         return total;
     }
 
@@ -49,7 +51,11 @@ public static int countEven(Collection<Integer> numbers) {
         // TODO:
         // Loop through the collection
         // If the number is even, increase count
-
+for(Integer even: numbers){
+    if(even % 2 == 0){
+        count++;
+    }
+}
         return count;
     }
 
@@ -65,7 +71,11 @@ public static int findMax(Collection<Integer> numbers) {
         // TODO:
         // Loop through numbers
         // Update max if current number is larger
-
+for(Integer newMax: numbers){
+if(newMax > max){
+    max = newMax;
+}
+}
         return max;
     }
 
@@ -80,8 +90,9 @@ public static boolean hasDuplicates(Collection<Integer> numbers) {
         // TODO:
         // Hint:
         // Compare the size of a collection with the size of a Set
+Set<Integer> diffNumbers = new HashSet<>(numbers);
 
-        return false;
+        return diffNumbers.size() !=numbers.size();
     }
 
 
@@ -96,7 +107,11 @@ public static int countOccurrences(Collection<Integer> numbers, int target) {
         // TODO:
         // Loop through numbers
         // If number equals target, increase count
-
+for(Integer nextNum: numbers){
+    if(nextNum == target){
+        count++;
+    }
+}
         return count;
     }
 
@@ -113,7 +128,12 @@ public static Collection<Integer> filterGreaterThanTwenty(Collection<Integer> nu
         // TODO:
         // Loop through numbers
         // Add numbers greater than 20 to result
-
+for(Integer overTwenty: numbers){
+    if(overTwenty > 20){
+        result.add(overTwenty);
+    }
+}
         return result;
+
     }
 }

src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java

@@ -1,5 +1,5 @@
 package CollectionsHackerrank;
-
+import  java.util.*;
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
@@ -22,10 +22,9 @@ public static void main(String[] args) {
         Output: [1,2,3,4,5]
         */
         public static List<Integer> removeDuplicates(List<Integer> numbers) {
-
             // TODO: Implement this method
 
-            return null;
+            return new ArrayList<>(new LinkedHashSet<>(numbers));
         }
 
         /*
@@ -37,10 +36,14 @@ public static List<Integer> removeDuplicates(List<Integer> numbers) {
         Output: {1=1, 2=2, 3=3}
         */
         public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
-
             // TODO: Implement this method
+            Map<Integer, Integer> frequency = new HashMap<>();
 
-            return null;
+            for (Integer num : numbers) {
+                frequency.put(num, frequency.getOrDefault(num, 0) + 1);
+            }
+
+            return frequency;
         }
 
         /*
@@ -52,8 +55,14 @@ public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
         Output: 5
         */
         public static Integer firstUnique(List<Integer> numbers) {
-
             // TODO: Implement this method
+            Map<Integer, Integer> frequency = countFrequency(numbers);
+
+            for (Integer num : numbers) {
+                if (frequency.get(num) == 1) {
+                    return num;
+                }
+            }
 
             return null;
         }
@@ -69,8 +78,19 @@ public static Integer firstUnique(List<Integer> numbers) {
         Output: true
         */
         public static boolean twoSum(List<Integer> numbers, int target) {
-
             // TODO: Implement this method
+            Set<Integer> seen = new HashSet<>();
+
+            for (Integer num : numbers) {
+
+                int complement = target - num;
+
+                if (seen.contains(complement)) {
+                    return true;
+                }
+
+                seen.add(num);
+            }
 
             return false;
         }
@@ -86,8 +106,7 @@ public static boolean twoSum(List<Integer> numbers, int target) {
         public static int countUniqueWords(List<String> words) {
 
             // TODO: Implement this method
-
-            return 0;
+            return new HashSet<>(words).size();
         }
 
         /*
@@ -99,10 +118,18 @@ public static int countUniqueWords(List<String> words) {
         Output: [4,3,2,1]
         */
         public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
-
             // TODO: Implement this method
+            Stack<Integer> stack = new Stack<>();
 
-            return null;
+            while (!queue.isEmpty()) {
+                stack.push(queue.poll());
+            }
+
+            while (!stack.isEmpty()) {
+                queue.add(stack.pop());
+            }
+
+            return queue;
         }
 
         /*
@@ -117,10 +144,26 @@ public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
         Output: false
         */
         public static boolean isBalanced(String expression) {
-
             // TODO: Implement this method
+            Stack<Character> stack = new Stack<>();
 
-            return false;
+            for (char c : expression.toCharArray()) {
+
+                if (c == '(') {
+                    stack.push(c);
+                }
+
+                if (c == ')') {
+
+                    if (stack.isEmpty()) {
+                        return false;
+                    }
+
+                    stack.pop();
+                }
+            }
+
+            return stack.isEmpty();
         }
 
         /*
@@ -132,10 +175,21 @@ public static boolean isBalanced(String expression) {
         Output: 3
         */
         public static Integer mostFrequent(List<Integer> numbers) {
-
             // TODO: Implement this method
+            Map<Integer, Integer> frequency = countFrequency(numbers);
 
-            return null;
+            int maxCount = 0;
+            Integer result = null;
+
+            for (Map.Entry<Integer, Integer> entry : frequency.entrySet()) {
+
+                if (entry.getValue() > maxCount) {
+                    maxCount = entry.getValue();
+                    result = entry.getKey();
+                }
+            }
+
+            return result;
         }
 
         /*
@@ -152,10 +206,19 @@ public static Integer mostFrequent(List<Integer> numbers) {
         }
         */
         public static Map<Integer, List<String>> groupByLength(List<String> words) {
-
             // TODO: Implement this method
+            Map<Integer, List<String>> map = new HashMap<>();
 
-            return null;
+            for (String word : words) {
+
+                int length = word.length();
+
+                map.putIfAbsent(length, new ArrayList<>());
+
+                map.get(length).add(word);
+            }
+
+            return map;
         }
 
         /*
@@ -169,10 +232,23 @@ public static Map<Integer, List<String>> groupByLength(List<String> words) {
         Output: 9
         */
         public static int maxSlidingWindowSum(List<Integer> numbers, int k) {
-
             // TODO: Implement this method
+            int maxSum = 0;
+            int windowSum = 0;
+
+            for (int i = 0; i < numbers.size(); i++) {
+
+                windowSum += numbers.get(i);
+
+                if (i >= k - 1) {
+
+                    maxSum = Math.max(maxSum, windowSum);
+
+                    windowSum -= numbers.get(i - k + 1);
+                }
+            }
 
-            return 0;
+            return maxSum;
         }
     }
 }

src/main/java/Iterable/Examples/ForEachLoopDemo.java

@@ -18,20 +18,24 @@ public static void main(String[] args) {
         // TODO:
         // Use a for-each loop to print each student name
 
+        for(String student: students) {
 
-        System.out.println("\nPrinting students in uppercase:");
-
+            System.out.println(student);
+        }
+        System.out.println();
         // TODO:
         // Use a for-each loop to print each name in uppercase
-
-
-        System.out.println("\nCount the number of students:");
-
-        int count = 0;
+        for(String student: students) {
+            System.out.println(student.toUpperCase());
+        }
+        System.out.println();
 
         // TODO:
         // Use a for-each loop to count how many students are in the list
-
+        int count = 0;
+for(String student: students) {
+   count++;
+}
         System.out.println("Total students: " + count);
     }
 }

src/main/java/Iterable/Examples/IteratorDemo.java

@@ -17,7 +17,7 @@ public static void main(String[] args) {
 
         System.out.println("Original list:");
         System.out.println(numbers);
-
+//Can you store multiple array lists in an iterator?
         // Create iterator
         Iterator<Integer> iterator = numbers.iterator();
 
@@ -26,7 +26,10 @@ public static void main(String[] args) {
         // TODO:
         // Use iterator.hasNext() and iterator.next()
         // Print each number
-
+while(iterator.hasNext()){
+  Integer num = iterator.next();
+    System.out.println(num);
+}
 
         System.out.println("\nRemoving odd numbers using Iterator");
 
@@ -35,7 +38,12 @@ public static void main(String[] args) {
         // TODO:
         // Use iterator to remove odd numbers
         // Remember: use iterator.remove()
-
+while(iterator.hasNext()){
+    Integer num = iterator.next();
+if(num % 2 !=0 ){
+    iterator.remove();
+}
+}
 
         System.out.println("\nUpdated list:");
         System.out.println(numbers);