Added solution to min_stack

Author: avidLearnerInProgress

min_stack_o(1).cpp

@@ -0,0 +1,57 @@
+class MinStack {
+public:
+    /** initialize your data structure here. */
+    stack<long double> s;
+    long min;
+    
+    MinStack() {
+        
+    }
+    
+    void push(long double x) {
+        if(s.empty()) { //if stack is empty just push and set it as min
+            s.push(x);
+            min = x;
+        }    
+        else{
+            if(x < min) { //if current value is less than current min, create flag in stack as 2 * x - min which will allow to traverse amongst next min while popping
+                s.push(2 * x - min);
+                min = x;
+            }
+            else
+                s.push(x); //just push current x
+        }
+    }
+    
+    void pop() {
+        if(!s.empty()){ //if stack is non empty
+            if(s.top() < min) { //if current top is less than min, this indicates that the top is flag. Which means that we update the min to next closest min and then pop the current top
+                min = 2 * min - s.top();
+                s.pop();
+            }
+            else { //else just pop
+                s.pop();
+            }
+        }
+    }
+    
+    int top() {
+        if(s.top() < min) { //if top is less than min 
+            return min;
+        }
+        else return s.top();
+    }
+    
+    int getMin() {
+        return min;
+    }
+};
+
+/**
+ * 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();
+ */