Min Stack

1. Title

2. Http address

https://leetcode.com/problems/min-stack/

3. The 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.

4 My code(AC)

•  1 public class MinStack {
   2
   3     // Accepted
   4     public LinkedList<Integer> stack = new LinkedList<Integer>();
   5     public LinkedList<Integer> min_stack = new LinkedList<Integer>();
   6
   7       public void push(int x) {
   8
   9               stack.offerFirst(x);
  10
  11               if ( min_stack.isEmpty() || x < min_stack.peekFirst()) {
  12                   min_stack.offerFirst(x);
  13               }else{
  14                   min_stack.offerFirst(min_stack.peekFirst());
  15               }
  16       }
  17
  18      public void pop() {
  19             stack.pollFirst();
  20             min_stack.pollFirst();
  21      }
  22
  23         public int top() {
  24             return stack.peekFirst();
  25         }
  26
  27         public int getMin() {
  28                 return min_stack.peekFirst();
  29         }
  30 }