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Leetcode Single queue using 2 stacks.java. Using Java implicitly named classes. Just to show that we can do Java without explicitly named classes
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| import java.util.ArrayList; | |
| import java.util.List; | |
| void main() { | |
| System.out.println("Hello, Java 22!"); | |
| QueueOperations queue = createQueue(createStack(), createStack()); | |
| queue.push(1); | |
| queue.push(2); | |
| queue.push(3); | |
| queue.pop(); | |
| queue.peek(); | |
| queue.pop(); | |
| queue.pop(); | |
| queue.isNotEmpty(); | |
| System.out.println("The end!"); | |
| } | |
| private QueueOperations createQueue(StackOperations stack1, StackOperations stack2) { | |
| return new QueueOperations() { | |
| public void push(int item) { | |
| stack1.push(item); | |
| } | |
| public int pop() { | |
| shiftStacks(); | |
| return stack2.pop(); | |
| } | |
| public int peek() { | |
| shiftStacks(); | |
| return stack2.peek(); | |
| } | |
| public boolean isEmpty() { | |
| return stack1.isEmpty() && stack2.isEmpty(); | |
| } | |
| public boolean isNotEmpty() { | |
| return stack1.isNotEmpty() || stack2.isNotEmpty(); | |
| } | |
| private void shiftStacks() { | |
| if (stack2.isEmpty()) { | |
| while (stack1.isNotEmpty()) { | |
| stack2.push(stack1.pop()); | |
| } | |
| } | |
| } | |
| }; | |
| } | |
| private StackOperations createStack() { | |
| List<Integer> elements = new ArrayList<>(); | |
| return new StackOperations() { | |
| public void push(int item) { | |
| elements.add(item); | |
| } | |
| public int pop() { | |
| return elements.removeLast(); | |
| } | |
| public int peek() { | |
| return elements.getLast(); | |
| } | |
| public boolean isEmpty() { | |
| return elements.isEmpty(); | |
| } | |
| public boolean isNotEmpty() { | |
| return !elements.isEmpty(); | |
| } | |
| }; | |
| } | |
| interface QueueOperations { | |
| void push(int item); | |
| int pop(); | |
| int peek(); | |
| boolean isEmpty(); | |
| boolean isNotEmpty(); | |
| } | |
| interface StackOperations { | |
| void push(int item); | |
| int pop(); | |
| int peek(); | |
| boolean isEmpty(); | |
| boolean isNotEmpty(); | |
| } |
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Put it into newly created Main.java and run:
java --enable-preview --source 22 Main.java