E

1525667761

tags: Stack

随便用一个data structure, implement stack.

#### Stack, 先入, 后出

- ArrayList: return/remove ArrayList的末尾项。

- 2 Queues

```

/*

LintCode

Implement Stack

Implement a stack. You can use any data structure inside a stack except stack itself to implement it.

Example

push(1)

pop()

push(2)

top() // return 2

pop()

isEmpty() // return true

push(3)

isEmpty() // return false

Tags Expand

Array Stack

*/

/*

Thoughts:

use arraylist and a index tracker - leng

push: add to end

pop: remove end

top: get end.

isEmpty: return length

*/

class Stack {

private ArrayList<Integer> list = new ArrayList<Integer>();

// Push a new item into the stack

public void push(int x) {

list.add(x);

}

// Pop the top of the stack

public void pop() {

if (list.size() > 0) {

list.remove(list.size() - 1);

}

}

// Return the top of the stack

public int top() {

if (list.size() > 0) {

return list.get(list.size() - 1);

}

return -1;

}

// Check the stack is empty or not.

public boolean isEmpty() {

return list.size() == 0;

}

}

```