Merge pull request #1088 from Rahul8691/Rahul8691-patch-2

Added Solution for LeetCode Problem No. 155

Author: Sirajmolla

LeetCode/155. Min Stack/Solution.java

@@ -0,0 +1,27 @@
+class MinStack {
+    int min = Integer.MAX_VALUE;
+    Stack<Integer> stack = new Stack<Integer>();
+    public void push(int x) {
+        // only push the old minimum value when the current 
+        // minimum value changes after pushing the new value x
+        if(x <= min){          
+            stack.push(min);
+            min=x;
+        }
+        stack.push(x);
+    }
+
+    public void pop() {
+        // if pop operation could result in the changing of the current minimum value, 
+        // pop twice and change the current minimum value to the last minimum value.
+        if(stack.pop() == min) min=stack.pop();
+    }
+
+    public int top() {
+        return stack.peek();
+    }
+
+    public int getMin() {
+        return min;
+    }
+}