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67 lines (58 loc) · 1.33 KB
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package com.williamfiset.algorithms.datastructures.stack;
import java.util.Arrays;
import java.util.EmptyStackException;
/**
* Array-based Stack
*
* A generic stack backed by a dynamically resizing array. Starts with
* capacity 16 and doubles when full. Push, pop, and peek are all O(1)
* amortized.
*
* Time: O(1) amortized for push, O(1) for pop and peek
* Space: O(n)
*
* @author liujingkun
*/
public class ArrayStack<T> implements Stack<T> {
private int size;
private int capacity;
private Object[] data;
public ArrayStack() {
capacity = 16;
data = new Object[capacity];
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public void push(T elem) {
if (size == capacity) {
increaseCapacity();
}
data[size++] = elem;
}
// Increase the capacity to store more elements.
private void increaseCapacity() {
capacity *= 2;
data = Arrays.copyOf(data, capacity);
}
@Override
@SuppressWarnings("unchecked")
public T pop() {
if (isEmpty()) throw new EmptyStackException();
T elem = (T) data[--size];
data[size] = null;
return elem;
}
@Override
@SuppressWarnings("unchecked")
public T peek() {
if (isEmpty()) throw new EmptyStackException();
return (T) data[size - 1];
}
}