Given a number , write a program to reverse this number using stack.
Examples:
Input : 365 Output : 563 Input : 6899 Output : 9986
We have already discussed the simple method to reverse a number in this post. In this post we will discuss about how to reverse a number using stack.
The idea to do this is to extract digits of the number and push the digits on to a stack. Once all of the digits of the number are pushed to the stack, we will start poping the contents of stack one by one and form a number.
As stack is a LIFO data structure, digits of the newly formed number will be in reverse order.
Below is the implementation of above idea:
C++
// CPP program to reverse the number // using a stack #include <bits/stdc++.h> using namespace std; // Stack to maintain order of digits stack <int> st; // Function to push digits into stack void push_digits(int number) { while (number != 0) { st.push(number % 10); number = number / 10; } } // Function to reverse the number int reverse_number(int number) { // Function call to push number's // digits to stack push_digits(number); int reverse = 0; int i = 1; // Popping the digits and forming // the reversed number while (!st.empty()) { reverse = reverse + (st.top() * i); st.pop(); i = i * 10; } // Return the reversed number formed return reverse; } // Driver program to test above function int main() { int number = 39997; // Function call to reverse number cout << reverse_number(number); return 0; } |
Java
// Java program to reverse the number // using a stack import java.util.Stack; public class GFG { // Stack to maintain order of digits static Stack<Integer> st= new Stack<>(); // Function to push digits into stack static void push_digits(int number) { while(number != 0) { st.push(number % 10); number = number / 10; } } // Function to reverse the number static int reverse_number(int number) { // Function call to push number's // digits to stack push_digits(number); int reverse = 0; int i = 1; // Popping the digits and forming // the reversed number while (!st.isEmpty()) { reverse = reverse + (st.peek() * i); st.pop(); i = i * 10; } // Return the reversed number formed return reverse; } // Driver program to test above function public static void main(String[] args) { int number = 39997; System.out.println(reverse_number(number)); } } // This code is contributed by Sumit Ghosh |
Python3
# Python3 program to reverse the # number using a stack # Stack to maintain order of digits st = []; # Function to push digits into stack def push_digits(number): while (number != 0): st.append(number % 10); number = int(number / 10); # Function to reverse the number def reverse_number(number): # Function call to push number's # digits to stack push_digits(number); reverse = 0; i = 1; # Popping the digits and forming # the reversed number while (len(st) > 0): reverse = reverse + (st[len(st) - 1] * i); st.pop(); i = i * 10; # Return the reversed number formed return reverse; # Driver Code number = 39997; # Function call to reverse number print(reverse_number(number)); # This code is contributed by mits |
C#
// C# program to reverse the number // using a stack using System; using System.Collections.Generic; class GFG { // Stack to maintain order of digits public static Stack<int> st = new Stack<int>(); // Function to push digits into stack public static void push_digits(int number) { while (number != 0) { st.Push(number % 10); number = number / 10; } } // Function to reverse the number public static int reverse_number(int number) { // Function call to push number's // digits to stack push_digits(number); int reverse = 0; int i = 1; // Popping the digits and forming // the reversed number while (st.Count > 0) { reverse = reverse + (st.Peek() * i); st.Pop(); i = i * 10; } // Return the reversed number formed return reverse; } // Driver Code public static void Main(string[] args) { int number = 39997; Console.WriteLine(reverse_number(number)); } } // This code is contributed by Shrikant13 |
PHP
<?php // PHP program to reverse the number // using a stack // Stack to maintain order of digits $st = array(); // Function to push digits into stack function push_digits($number) { global $st; while ($number != 0) { array_push($st, $number % 10); $number = (int)($number / 10); } } // Function to reverse the number function reverse_number($number) { global $st; // Function call to push number's // digits to stack push_digits($number); $reverse = 0; $i = 1; // Popping the digits and forming // the reversed number while (!empty($st)) { $reverse = $reverse + ($st[count($st) - 1] * $i); array_pop($st); $i = $i * 10; } // Return the reversed number formed return $reverse; } // Driver Code $number = 39997; // Function call to reverse number echo reverse_number($number); // This code is contributed by mits ?> |
Output:
79993
Time Complexity: O( logN )
Auxiliary Space: O( logN ), Where N is the input number.
This article is contributed by Rohit Thapliyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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