Create 225_Implement_Stack_using_Queues.cc

cpppy · web-flow · commit ded340e7a1ba · 2016-09-18T14:36:58.000+08:00
diff --git a/225_Implement_Stack_using_Queues.cc b/225_Implement_Stack_using_Queues.cc
@@ -0,0 +1,66 @@
+class Stack {
+public:
+    queue<int> main;
+    queue<int> temp;
+    // Push element x onto stack.
+    void push(int x) {
+        main.push(x);
+    }
+
+    // Removes the element on top of the stack.
+    void pop() {
+        if(!main.empty()){
+            while(main.size()>1){
+                int x=main.front();
+                main.pop();
+                temp.push(x);
+            }
+            main.pop();
+        }
+        else{
+            int s=temp.size();
+            int i=0;
+            while(i<s-1){
+                int x=temp.front();
+                temp.pop();
+                temp.push(x);
+                i++;
+            }
+            temp.pop();
+        }
+    }
+
+    // Get the top element.
+    int top() {
+        if(!main.empty()){
+            while(main.size()>1){
+                int x=main.front();
+                main.pop();
+                temp.push(x);
+            }
+            return main.front();
+        }
+        else{
+            int s=temp.size();
+            int i=0;
+            while(i<s-1){
+                int x=temp.front();
+                temp.pop();
+                temp.push(x);
+                i++;
+            }   
+            int y=temp.front();
+            temp.pop();
+            temp.push(y);
+            return y;
+        }
+    }
+
+    // Return whether the stack is empty.
+    bool empty() {
+        if(main.empty() && temp.empty())  return true;
+        else return false;
+        
+    }
+
+};
