programming-examples/java/Data_Structures/QueueMin.java

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Java
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2019-11-15 12:59:38 +01:00
import java.util.*;
public class QueueMin<E extends Comparable<E>> {
List<E[]> s1 = new ArrayList<>();
List<E[]> s2 = new ArrayList<>();
E min(E a, E b) {
return a.compareTo(b) < 0 ? a : b;
}
public E min() {
if (s1.isEmpty())
return s2.get(s2.size() - 1)[1];
if (s2.isEmpty())
return s1.get(s1.size() - 1)[1];
return min(s1.get(s1.size() - 1)[1], s2.get(s2.size() - 1)[1]);
}
public void addLast(E x) {
E minima = x;
if (!s1.isEmpty()) {
minima = min(minima, s1.get(s1.size() - 1)[1]);
}
s1.add((E[]) new Comparable[]{x, minima});
}
public E removeFirst() {
if (s2.isEmpty()) {
E minima = null;
while (!s1.isEmpty()) {
E x = s1.remove(s1.size() - 1)[0];
minima = minima == null ? x : min(minima, x);
s2.add((E[]) new Comparable[]{x, minima});
}
}
return s2.remove(s2.size() - 1)[0];
}
// Usage example
public static void main(String[] args) {
QueueMin<Integer> q = new QueueMin<>();
q.addLast(2);
q.addLast(3);
System.out.println(2 == q.min());
q.removeFirst();
System.out.println(3 == q.min());
q.addLast(1);
System.out.println(1 == q.min());
}
}