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1]. DSA/1]. Data Structures/10]. Queue/C++/_01)_implementation_of_queue_using_linked_list.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+class node
+	{
+		public:
+		int data;
+		node* next;
+		node(int x)
+			{
+				data = x;
+				next = NULL;
+			}
+	};
+
+class que
+	{
+		node* front;
+		node* back;
+
+		public:
+
+		que()
+			{
+				front = NULL;
+				back = NULL;	
+			}
+
+		void push(int x);
+		void pop();
+		int peek();
+		bool isempty();
+	};
+
+void que::push(int x)
+	{
+		node* n = new node(x);
+
+		if(isempty())
+			{
+				front = n;
+				back = n;
+			}
+
+		back->next = n;
+		back = n;
+
+	}
+
+void que::pop()
+	{
+		if(isempty())
+			{
+				cout<<"Queue is empty";
+				return ; 
+			}
+		node* todelete = front;
+		front = front->next;
+		delete todelete;
+	}
+
+int que::peek()
+	{
+		if(isempty())
+			{
+				cout<<"Queue is empty";
+				exit(1);
+			}
+		return front->data;
+	}
+
+bool que::isempty()
+	{
+		if(front == NULL)
+			{
+				return true;
+			}
+		else{return false;}
+	}
+
+int main()
+{
+	que q;
+	int n,m,x;
+
+	cin>>n;
+	for(int i=0;i<n;i++)
+		{
+			cin>>x;
+			q.push(x);
+		}
+
+	while(!q.isempty())	
+		{
+			cout<<q.peek()<<" ";
+			q.pop();
+		}
+
+	return 0;
+}

1]. DSA/1]. Data Structures/10]. Queue/C++/_02)_implementation_of_queue_using_single_stack.cpp

@@ -0,0 +1,62 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class que
+	{
+		stack<int>s1;
+
+		public:
+
+		void push(int x)
+			{
+				s1.push(x);
+			}
+
+		int pop()
+			{
+				if(s1.empty())
+					{
+						cout<<"Empty Queue";
+						return -1;
+					}
+
+				int x = s1.top();
+				s1.pop();
+
+				if(s1.empty())
+					{
+						return x;
+					}
+				int item = pop();
+				s1.push(x);
+				return item;
+
+			}
+
+		bool isempty()
+			{
+				if(s1.empty()){ return true;}
+				return false;
+			}	
+
+	};
+
+int main()
+{
+	que q;
+	int n,x;
+	cin>>n;
+
+	for(int i=0;i<n;i++)
+		{
+			cin>>x;
+			q.push(x);
+		}
+
+	while(!q.isempty())
+		{
+			cout<<q.pop()<<" ";
+		}
+
+	return 0;
+}

1]. DSA/1]. Data Structures/10]. Queue/C++/_03)_queue_implem_using_2_stack.cpp

@@ -0,0 +1,63 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class que
+	{
+		stack<int>s1;
+		stack<int>s2;
+
+		public:
+
+		void push(int x)
+			{
+				s1.push(x);
+			}
+
+		int pop()
+			{
+				if(s1.empty() and s2.empty())
+					{
+						cout<<"Empty Queue";
+						return -1;
+					}
+
+				if(s2.empty())
+					{
+						while(!s1.empty())
+							{
+								s2.push(s1.top());
+								s1.pop();
+							}
+					}
+				int topval = s2.top();
+				s2.pop();
+				return topval;
+			}
+
+		bool isempty()
+			{
+				if(s1.empty() and s2.empty()){ return true;}
+				return false;
+			}	
+
+	};
+
+int main()
+{
+	que q;
+	int n,x;
+	cin>>n;
+
+	for(int i=0;i<n;i++)
+		{
+			cin>>x;
+			q.push(x);
+		}
+
+	while(!q.isempty())
+		{
+			cout<<q.pop()<<" ";
+		}
+
+	return 0;
+}