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ArrayStack.java
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68 lines (57 loc) · 1.44 KB
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package stack;
public class ArrayStack<T> implements Stack<T> {
private T[] items; // 数组
private int top; // 栈中元素的个数（或者说是栈顶指针）
private int capacity; // 栈的容量
public ArrayStack(int capacity) {
this.capacity = capacity;
this.items = (T[]) new Object[capacity];
this.top = 0;
}
// T(N)=O(1)
@Override
public boolean push(T item) {
// 数组空间不足，无法push
if (top == capacity) {
return false;
}
// size为待push的位置
items[top] = item;
top++;
return true;
}
// T(N)=O(1)
@Override
public T pop() {
// 数组为空，无法pop
if (top == 0) {
return null;
}
T item = items[top -1];
top--;
return item;
}
// T(N)=O(1)
@Override
public T peek() {
if (top == 0) {
return null;
}
return items[top -1];
}
public static void main(String[] args) {
ArrayStack<String> stack = new ArrayStack<>(4);
stack.push("A");
stack.push("B");
stack.push("C");
stack.push("D");
System.out.println(stack.peek());
stack.pop();
System.out.println(stack.peek());
stack.pop();
stack.pop();
stack.pop();
stack.pop();
System.out.println(stack.peek());
}
}