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StackAndQueueConvert.java
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86 lines (75 loc) · 2.31 KB
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import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
public class StackAndQueueConvert {
public static class TwoStackQueue {
private Stack<Integer> stackPush;
private Stack<Integer> stackPop;
public TwoStackQueue() {
stackPush = new Stack<Integer>();
stackPop = new Stack<Integer>();
}
public void push(int obj) {
stackPush.push(obj);
}
public Integer poll() {
if (stackPop.isEmpty() && stackPush.isEmpty()) {
throw new RuntimeException("Queue is empty!");
} else if (stackPop.isEmpty()) {
while (!stackPush.isEmpty()) {
stackPop.push(stackPush.pop());
}
}
return stackPop.pop();
}
public int peek() {
if (stackPop.isEmpty() && stackPush.isEmpty()) {
throw new RuntimeException("Queue is empty!");
} else if (stackPop.isEmpty()) {
while (!stackPush.isEmpty()) {
stackPop.push(stackPush.pop());
}
}
return stackPop.peek();
}
}
public static class TwoQueueStack {
private Queue<Integer> queue;
private Queue<Integer> help;
public TwoQueueStack() {
queue = new LinkedList<Integer>();
help = new LinkedList<Integer>();
}
public void push(int obj) {
queue.add(obj);
}
public int peek() {
if (queue.isEmpty()) {
throw new RuntimeException("Stack is empty!");
}
while (queue.size() != 1) {
help.add(queue.poll());
}
int res = queue.poll();
help.add(res);
swap();
return res;
}
public int pop() {
if (queue.isEmpty()) {
throw new RuntimeException("Stack is empty!");
}
while (queue.size > 1) {
help.add(queue.poll());
}
int value = queue.poll();
swap();
return value;
}
private void swap() {
Queue<Integer> tmp = help;
help = queue;
queue = tmp;
}
}
}