Leetcode - Min Stack

Question

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) – Push element x onto stack.
• pop() – Removes the element on top of the stack.
• top() – Get the top element.
• getMin() – Retrieve the minimum element in the stack.

Note

Your MinStack object will be instantiated and called as such:

 MinStack obj = new MinStack();
 obj.push(x);
 obj.pop();
 int param_3 = obj.top();
 int param_4 = obj.getMin();

Java Code

public class MinStack {
    /** initialize your data structure here. */
    class Node {
        int val;
        Node next;
        Node(int x, Node n) {
            val = x; 
            next = n;
        }
    }

    /** * 实现方式： * 同时维护两个链表，一个用于存储栈内的数据，一个用于储存当前栈内的最小值， * 且两者的push和pop操作保持同步 */
    Node head = null;
    Node minhead = new Node(Integer.MAX_VALUE, null);

    public MinStack() {

    }

    public void push(int x) {
        head = new Node(x, head);
        if(x < minhead.val)
            minhead = new Node(x, minhead);
        else 
            minhead = new Node(minhead.val, minhead);
    }

    public void pop() {
        head = head.next;
        minhead = minhead.next;
    }

    public int top() {
        return head.val;
    }

    public int getMin() {
        return minhead.val;
    }
}