Min Stack

Change-Id: I9e549f77593c9dc1690a2620a8de952d3e287cad

Author: applewjg

MinStack.java

@@ -0,0 +1,33 @@
+/*
+ Author:     King, [email protected]
+ Date:       Nov 14, 2014
+ Problem:    Min Stack 
+ Difficulty: Easy
+ Source:     https://oj.leetcode.com/problems/min-stack/
+ Notes:
+ 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.
+*/
+
+class MinStack {
+    private Stack<Integer> stack = new Stack<>();
+    private Stack<Integer> minStack = new Stack<>();
+    public void push(int x) {
+      stack.push(x);
+      if (minStack.isEmpty() || x <= minStack.peek()) {
+         minStack.push(x);
+      }
+    }
+    public void pop() {
+      if (stack.pop().equals(minStack.peek())) minStack.pop();
+    }
+    public int top() {
+      return stack.peek();
+    }
+    public int getMin() {
+      return minStack.peek();
+    }
+}