Glenntyson java collections

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) {
@@ -21,7 +22,6 @@ public static void main(String[] args) {
         System.out.println("Contains duplicates? " + hasDuplicates(numbers));
     }
 
-
     /*
      PROBLEM 1
      Return the sum of all numbers in the collection
@@ -30,14 +30,13 @@ public static int sum(Collection<Integer> numbers) {
 
         int total = 0;
 
-        // TODO:
-        // Loop through the collection
-        // Add each number to total
+        for (Integer num : numbers) {
+            total += num;
+        }
 
         return total;
     }
 
-
     /*
      PROBLEM 2
      Count how many numbers are even
@@ -46,14 +45,15 @@ public static int countEven(Collection<Integer> numbers) {
 
         int count = 0;
 
-        // TODO:
-        // Loop through the collection
-        // If the number is even, increase count
+        for (Integer num : numbers) {
+            if (num % 2 == 0) {
+                count++;
+            }
+        }
 
         return count;
     }
 
-
     /*
      PROBLEM 3
      Find the largest number in the collection
@@ -62,29 +62,26 @@ public static int findMax(Collection<Integer> numbers) {
 
         int max = Integer.MIN_VALUE;
 
-        // TODO:
-        // Loop through numbers
-        // Update max if current number is larger
+        for (Integer num : numbers) {
+            if (num > max) {
+                max = num;
+            }
+        }
 
         return max;
     }
 
-
     /*
      PROBLEM 4
      Return true if the collection contains duplicates
      Return false otherwise
     */
     public static boolean hasDuplicates(Collection<Integer> numbers) {
 
-        // TODO:
-        // Hint:
-        // Compare the size of a collection with the size of a Set
+        return numbers.size() != new HashSet<>(numbers).size();
 
-        return false;
     }
 
-
     /*
      PROBLEM 5
      Count how many times a target value appears
@@ -93,14 +90,15 @@ public static int countOccurrences(Collection<Integer> numbers, int target) {
 
         int count = 0;
 
-        // TODO:
-        // Loop through numbers
-        // If number equals target, increase count
+        for (Integer num : numbers) {
+            if (num == target) {
+                count++;
+            }
+        }
 
         return count;
     }
 
-
     /*
      BONUS PROBLEM
      Create and return a new collection
@@ -110,10 +108,12 @@ public static Collection<Integer> filterGreaterThanTwenty(Collection<Integer> nu
 
         Collection<Integer> result = new ArrayList<>();
 
-        // TODO:
-        // Loop through numbers
-        // Add numbers greater than 20 to result
+        for (Integer num : numbers) {
+            if (num > 20) {
+                result.add(num);
+            }
+        }
 
         return result;
     }
-}
+}

src/main/java/Collections/Quiz/KnowledgeCheck.md

@@ -16,7 +16,7 @@ A. `Collection` is a class
 B. `Collection` extends `List`  
 C. `Collection` is the root interface for most collection types  
 D. `Collection` only stores key-value pairs  
-
+C
 ---
 
 ## Question 2
@@ -36,7 +36,7 @@ A. 0
 B. 1
 C. 3
 D. 30
-
+C
 ---
 
 ## Question 3
@@ -47,7 +47,7 @@ A. `search()`
 B. `exists()`
 C. `contains()`
 D. `check()`
-
+C
 ---
 
 ## Question 4
@@ -69,7 +69,7 @@ A. `[Alex, Jordan]`
 B. `[Jordan]`
 C. `[Alex]`
 D. `[]`
-
+B
 ---
 
 ## Question 5
@@ -80,7 +80,7 @@ A. `add()`
 B. `addAll()`
 C. `insertAll()`
 D. `merge()`
-
+B
 ---
 
 ## Question 6
@@ -97,7 +97,7 @@ A. `true`
 B. `false`
 C. `0`
 D. Compilation error
-
+A
 ---
 
 ## Question 7
@@ -108,7 +108,7 @@ A. `removeAll()`
 B. `deleteAll()`
 C. `clear()`
 D. `reset()`
-
+C
 ---
 
 ## Question 8
@@ -131,7 +131,7 @@ A. `5 10 15`
 B. `15 10 5`
 C. `0 1 2`
 D. Compilation error
-
+A
 ---
 
 ## Question 9
@@ -142,7 +142,7 @@ A. Elements can be added
 B. Elements can be removed
 C. Indexed access using `.get(index)`
 D. Elements can be iterated using a loop
-
+C
 ---
 
 ## Question 10
@@ -157,6 +157,6 @@ A. It automatically sorts the collection
 B. It prevents duplicates
 C. It allows flexibility to change implementations later
 D. It forces the collection to be synchronized
-
+C
 ```
 ```