Create MinStack.java

Author: carpeventus

code/offer/src/Chap4/MinStack.java

@@ -0,0 +1,45 @@
+package Chap4;
+
+import java.util.LinkedList;
+
+public class MinStack {
+
+    private LinkedList<Integer> stack;
+    private LinkedList<Integer> minStack;
+
+    /** initialize your data structure here. */
+    public MinStack() {
+        stack=new LinkedList<>();
+        minStack = new LinkedList<>();
+    }
+
+    public void push(int x) {
+        stack.push(x);
+        if (minStack.isEmpty() || x <= minStack.peek()) {
+            minStack.push(x);
+        }
+    }
+
+    public void pop() {
+        if (stack.isEmpty()) {
+            return;
+        }
+        if (stack.pop().equals(minStack.peek())) {
+            minStack.pop();
+        }
+    }
+
+    public int top() {
+        if (stack.isEmpty()) {
+            return -1;
+        }
+        return stack.peek();
+    }
+
+    public int min() {
+        if (minStack.isEmpty()) {
+            return -1;
+        }
+        return minStack.peek();
+    }
+}