Day 2 – String Reversal and Palindrome
Part A – String Reversal
Question - Given a string, write a program to return a new string with reversed order of characters.
JavaScript Implementation
Solution 1
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Step 1: Strings are immutable (in JavaScript), hence convert it into array.
// Step 2: Run a loop from 0 to (size of array)/2 and interchange the element at i index with element at position size-1-i
// Step 3: Join the array to form a string
function strRev (str) {
var i, j, temp, len = str.length;
// Strings are immutable in javascript, hence we convert the string into an array
str = str.split('');
// Reverse the array elements by interchanging the elements which are equidistant from start and end
for (i=0, j=len-1; i<=len/2; i++, j--) {
temp = str[i];
str[i] = str[j];
str[j] = temp;
}
// Join the reversed array into a string
str = str.join('');
// Return the reversed string
return str;
}
console.log(strRev('Hello!'));
Solution 2
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Step 1: Declare a temporary array, say tempArr[]
// Step 2: Run a loop from size-1 to 0 and add corresponding character of string to the tempArr[] from beginning
// Method 2.1 (Add using index)
// for (i=0, j=len-1; i<len; i++, j--) {
// tempArr[i] = str[j];
// }
// Method 2.2 (Add using `push()` )
// for (j=len-1; j>=0; j--) {
// tempArr.push(str[j]);
// }
// Step 3: Join the elements of the tempArr[] to form a string
function strRev (str) {
var i, j,
len = str.length,
tempArr = [];
// Read string in reverse order and store each letter in the array
for (j=len-1; j>=0; j--) {
tempArr.push(str[j]);
}
// Join the tempArr to convert it into a string
tempArr = tempArr.join('');
// Return tempArr
return tempArr;
}
console.log(strRev('Hello!'));
Solution 3
/**
* @author MadhavBahl
* @date 21/12/2018
*/
function strRev (str) {
var i, j,
len = str.length,
tempArr = [];
// Read string in reverse order and store each letter in the array
for (i=0, j=len-1; i<len; i++, j--) {
tempArr[i] = str[j]; // You can use push() instead of assigning by index
}
// Join the tempArr to convert it into a string
tempArr = tempArr.join('');
// Return tempArr
return tempArr;
}
console.log(strRev('Hello!'));
Solution 4
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Step 1: Split the given string into array
// Step 2: Reverse the array using reverse() function
// Step 3: Join the reversed array to form a string
// This solution works with JS only (or any other language which supports in built methods)
function strRev (str) {
// Convert str to array
// Reverse the array
// Join the array to form a string
// let arr = str.split('');
// arr.reverse();
// return arr.join('');
// One Liner answer
return str.split('').reverse().join('');
}
console.log(strRev('Hello!'));
Solution 5
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Step 1: Declare an empty string, say reverse = ''
// Step 2: Run a loop from 0 to length of string
// Step 3: For each letter of original string, concatenate reverse with it. (concatenate each element of string with reverse string, such that element gets concatenated before the current reverse string)
// Using basic string concatenation
function strRev (str) {
// Initialize an empty string "Reverse"
let reverse = '';
for (i=0; i<str.length; i++) {
// for each letter of original string, concatenate reverse with it
reverse = str[i] + reverse;
}
return reverse;
}
console.log(strRev('Hello!'));
Solution 6
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Method 5 -- Using reduce helper
// Using reduce helper function (JS only)
function strRev(str) {
// return str.split('').reduce((reversed, character) => {
// return character+reversed;
// }, '');
// One Liner
return str.split('').reduce((rev, letter) => letter + rev, '');
}
console.log(strRev('Hello!'));
Java Implementation
Solution 1
/**
* @author MadhavBahl
* @date 21/12/2018
*/
import java.util.Scanner;
public class Reverse {
public static void main(String[] args) {
System.out.println("/* ===== String Reversal ===== */");
System.out.print("\nPlease enter the string: ");
Scanner input = new Scanner(System.in);
String str = input.next();
String reversed = "";
for (int i=0; i<str.length(); i++) {
reversed = str.charAt(i) + reversed;
}
System.out.println("Reversed String: " + reversed);
}
}
[Solution by @nomitpahuja] (./Java/ReverseString.java)
/*
* @author Nomit Pahuja
* date: 29/01/2018
*/
import java.util.Scanner;
public class ReverseString {
public static String reverseString(String word, int length){
String reverseWord = "";
for(int i=length-1; i>=0; i--){
reverseWord += word.charAt(i);
}
return reverseWord;
}
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("Enter the String: ");
String word = input.next();
int length = word.length();
String reverse = reverseString(word, length);
System.out.println("The reversed string is: " + reverse);
input.close();
}
}
Solution by @malhotra1432
/* @date 03/10/2020
* @author Prabhat Malhotra
*/
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;
/*
* Solution A - String Reversal
*/
public class StringReversal {
public String stringReversal(String randomString) {
byte[] randomStringAsByteArray = randomString.getBytes();
byte[] byteArrayResult = new byte[randomStringAsByteArray.length];
for (int i = 0; i < byteArrayResult.length; i++) {
byteArrayResult[i] = randomStringAsByteArray[randomStringAsByteArray.length - i - 1];
}
return new String(byteArrayResult);
}
}
/*
* Test A - String Reversal
*/
class StringReversalTest {
@Test
public void reverseString() {
String randomString = "prabhat";
StringReversal stringReversal = new StringReversal();
System.out.println("The reverse of string " + randomString + " is " + stringReversal.stringReversal(randomString));
}
}
/*
* Solution B - Palindrome Check
*/
class PalindromeCheck {
public boolean palindromeChek(String randomString) {
StringReversal stringReversal = new StringReversal();
String reversedString = stringReversal.stringReversal(randomString);
return reversedString.equals(randomString);
}
}
/*
* Test B - Palindrome Check
*/
class PalindromeCheckTest {
@Test
public void shouldBePalindrome() {
String randomString = "LOL";
PalindromeCheck palindromeCheck = new PalindromeCheck();
if (palindromeCheck.palindromeChek(randomString)) {
System.out.println(randomString + " is a palindrome");
}
assertTrue(palindromeCheck.palindromeChek(randomString));
}
@Test
public void shouldNotToBePalindrome() {
String randomString = "HOT";
PalindromeCheck palindromeCheck = new PalindromeCheck();
if (!palindromeCheck.palindromeChek(randomString)) {
System.out.println(randomString + " is not a palindrome");
}
assertFalse(palindromeCheck.palindromeChek(randomString));
}
}
C++ Implementation
Solution by @imkaka
/*
* @author: imkaka
* @date : 21/12/2018
*/
#include<iostream>
#include<string>
using namespace std;
int main(){
string str;
cin >> str ;
int size = str.size();
for(int i = 0; i< size/2; i++)
{
char temp = str[i];
str[i] = str[size-i-1];
str[size-1-i] = temp;
}
cout << str << endl;
return 0;
}
/*
*@author: profgrammer
*@date: 30-12-2018
*/
#include <bits/stdc++.h>
using namespace std;
int main() {
string s;
cin>>s;
// method 1: print the string in reverse order
cout<<"The reversed string is: ";
for(int i = s.size()-1;i >= 0;i--) cout<<s[i];
cout<<endl;
// method 2: swap characters at either end
string s1 = s;
for(int i = 0, j = s1.size()-1;i <= j;i++, j--){
char temp = s1[i];
s1[i] = s1[j];
s1[j] = temp;
}
cout<<"The reversed string is: "<<s1<<endl;
// method 3: library functions
s1 = s;
reverse(s1.begin(), s1.end());
cout<<"The reversed string is: "<<s1<<endl;
// to check if the string is a palindrome, we need to check if it is equal to its reverse.
if(s.compare(s1) == 0) cout<<"The string is a palindrome"<<endl;
else cout<<"The string is not a palindrome\n";
}
Solution by @divyakhetan
/**
* @author:divyakhetan
* @date: 30/12/2018
*/
#include<bits/stdc++.h>
using namespace std;
int main(){
string s;
cin >> s;
reverse(s.begin(), s.end());
cout <<s;
return 0;
}
Python Implementation
Solution 1
'''
* @author: ashwek
* @date: 21/12/2018
'''
Str = input("Enter a string : ")
print("Reverse of", Str, "=", Str[::-1])
C++ Implementation
reverse.cpp
/**
* @author: Rajdeep Roy Chowdhury<rrajdeeproychowdhury@gmail.com>
* @github: https://github.com/razdeep
* @date: 21/12/2018
*/
#include<iostream>
using namespace std;
string strRev(const string& s)
{
static string temp=s;
int k=0;
for(int i=s.size()-1;i>=0;i--)
{
temp[k++]=s[i];
}
return temp;
}
int main()
{
string s="Hello";
string rev=strRev(s);
cout<<rev<<endl;
return 0;
}
C Implementation
Solution 1
/**
* @author : ashwek
* @date : 21/12/2018
*/
#include<stdio.h>
#include<string.h>
void reverse(char Str[]){
char temp;
int i;
for(i=0; i<(strlen(Str)/2); i++){
temp = Str[i];
Str[i] = Str[strlen(Str)-i-1];
Str[strlen(Str)-i-1] = temp;
}
}
void main(){
char Str[50], Rev[50];
printf("Enter a string = ");
scanf("%s", Str);
strcpy(Rev, Str);
reverse(Rev);
printf("Reverse = %s", Rev);
}
Ruby Implementation
reverse.rb
=begin
@author: aaditkamat
@date: 22/12/2018
=end
def short_solution(str)
if str.class != String or str === nil
return false
end
str.reverse
end
def long_solution_iterative(str)
if str.class != String or str === nil
return false
end
reverse = ''
i = 0
until i >= str.length do
reverse.insert(0, str[i])
i += 1
end
reverse
end
def long_solution_recursive(str)
if str.class != String or str === nil
return false
end
if str === ''
return ''
end
temp = str[0]
str[0] = str[-1]
str[-1] = temp
return long_solution(str[1..-2])
end
Part B – Palindrome Check
Question - Given a string, write a function which prints whether or not the given string is a Palindrome
JavaScript Implementation
Solution 1
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Method 1 (Check the equidistant characters)
// Step 1: Set a flag variable ( = 1 )
// Step 2: Run a loop from 0 to stringLength/2
// Step 3: In each iteration check whether character at ith position is equal to the character at length-i-1 position.
// Step 4: If the condition is satisfied even once, set the flag to 0
// Step 5: After the iterations are over, if the flag = 1, print "Palindrome" else print "Not Palindrome"
function isPalindrome (str) {
let i, len = str.length, flag = 1;
// Check the equidistant characters
for (i=0; i>=len/2; i++) {
if (str[i] !== str[len-1-i]) {
flag = 0;
break;
}
}
// Print the result based on flag
if (flag === 1) {
console.log("The given string \"" + str + "\" is a palindrome");
} else {
console.log("The given string \"" + str + "\" is not a palindrome");
}
}
isPalindrome("hello");
isPalindrome("level");
Solution 2
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// Step 1: Find the reverse of the given string
// Step 2: If reverse is equal to original string, print "Palindrome", else print "Not Palindrome".
function isPalindrome (str) {
let reversed = str.split('').reverse().join('');
if (str === reversed) {
console.log("The given string \"" + str + "\" is a palindrome");
} else {
console.log("The given string \"" + str + "\" is not a palindrome");
}
}
isPalindrome('hello');
isPalindrome('level');
Solution 3 – One Liner
/**
* @author MadhavBahl
* @date 21/12/2018
*/
// One Liner
function isPalindrome (str) {
(str === (str.split('').reverse().join(''))) ? console.log("Palindrome") : console.log("Not Palindrome");
}
isPalindrome('hello');
isPalindrome('level');
Java Implementation
Solution 1
/**
* @author MadhavBahl
* @date 21/12/2018
*/
import java.util.Scanner;
public class Palindrome {
public static void main (String[] args) {
System.out.println("/* ===== Palindrome Check ===== */");
System.out.print("\nPlease enter a string to check: ");
// Read the string
Scanner input = new Scanner(System.in);
String str = input.next();
int size = str.length(), flag =1;
// Check whether it is palindrome
for (int i=0, j=size-1; i<=size/2; i++, j--) {
// Check whether the characters equidistant from start and end are same or not
if (str.charAt(i) != str.charAt(j)) {
flag = 0;
break;
}
}
// Print results according to flag
if (flag == 0) {
System.out.println("The given string \"" + str + "\" is not a palindrome");
} else {
System.out.println("The given string \"" + str + "\" is a palindrome");
}
}
}
Solution 2
/**
* @author MadhavBahl
* @date 21/12/2018
*/
import java.util.Scanner;
// Method 2: Check whether reversed string is equal to the original string
public class Palindrome2 {
public static void main (String[] args) {
System.out.println("/* ===== Palindrome Check ===== */");
System.out.print("\nPlease enter a string to check: ");
// Read the string
Scanner input = new Scanner(System.in);
String str = input.next();
String reversed = "";
int size = str.length();
// Reverse the string
for (int i=0; i<str.length(); i++) {
reversed = str.charAt(i) + reversed;
}
// Check if the reversed string is same as the original string
if (str.equals(reversed)) {
System.out.println ("The given string \"" + str + "\" is a Palindrome");
} else {
System.out.println ("The given string \"" + str + "\" is not a Palindrome");
}
}
}
Solution 3
/**
* @date 29th jan 2019
* @author nehabindal
*/
import java.util.*;
public class day22 {
public static void main(String[] args)
{
System.out.println("Input a string to check it it's a pallindrome or not");
Scanner sc = new Scanner(System.in);
String st = sc.nextLine();
int l = st.length();
int flag=0;
for(int i=0;i<l/2;i++)
{
if(st.charAt(i)!=st.charAt(l-1-i))
{
flag=1;
}
}
if(flag==1)
{
System.out.println("Not a pallindrome");
}
else{
System.out.println("Yay a pallindorme");
}
}
}
Solution by @nomitpahuja
/*
* @author Nomit Pahuja
* date: 29/01/2019
*/
import java.util.Scanner;
public class Palindrome {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("Enter the String: ");
String word = input.next();
word = word.toLowerCase();
int size = word.length();
int flag = 1;
//checking if string is palindrome or not
for(int i = 0, j = size-1; i<size/2; i++, j--){
if(word.charAt(i) != word.charAt(j)){
flag = 0;
}
}
//print if string is palindrome or not
if(flag == 0){
System.out.println("The given string is not a palindrome.");
} else {
System.out.println("The given string is a palindrome.");
}
input.close();
}
}
C++ Implementation
Solution by @imkaka
/*
* @author: imkaka
* @date : 21/12/2018
*/
#include<iostream>
#include<string>
using namespace std;
int main(){
string str;
cin >> str ;
int size = str.size();
bool flag = false;
for(int i = 0; i< size/2; i++)
{
if(str[i] != str[size-i-1])
{
flag = true;
break;
}
}
if(!flag)
cout << str <<" is a Palindrome!!" << endl;
else
cout << str << " is NOT a Palindrome!" << endl;
return 0;
}
Solution by @divyakhetan
/**
* @author:divyakhetan
* @date: 30/12/2018
*/
#include<bits/stdc++.h>
using namespace std;
int main(){
string s;
cin >> s;
string t = s;
reverse(s.begin(), s.end());
if(s.compare(t) == 0) cout << "Palindrome!";
else cout << "Not a palindrome";
return 0;
}
Python Implementation
Solution 1
'''
* @author: ashwek
* @date: 21/12/2018
'''
Str = input("Enter a string : ")
print(Str, "is", end=" ")
if( Str != Str[::-1] ):
print("Not", end=" ")
print("Palindrome")
C Implementation
Solution 1
/**
* @author : ashwek
* @date : 21/12/2018
*/
#include<stdio.h>
#include<string.h>
void reverse(char Str[]){
char temp;
int i;
for(i=0; i<(strlen(Str)/2); i++){
temp = Str[i];
Str[i] = Str[strlen(Str)-i-1];
Str[strlen(Str)-i-1] = temp;
}
}
void main(){
char Str[50], Rev[50];
printf("Enter a string = ");
scanf("%s", Str);
strcpy(Rev, Str);
reverse(Rev);
printf("%s is ", Str);
if( strcmp(Str, Rev) != 0)
printf("not ");
printf("palindrome\n");
}
Python implementation
String reversing and pallindrome checking(./python3/String_and_pallindrome.py)
"""
* @author Shashank
* @date 21/12/2018
"""
a=input("Enter the input string:")
d=a.replace(" ","")
c=list(d)
c.reverse()
e="".join(c)
if d==e:
print("String is pallindrome")
else:
print("Not a pallindrome")
Ruby implementation
palindrome.rb
=begin
@author: aaditkamat
@date: 22/12/2018
=end
require './reverse'
def palindrome(str)
str != nil and str === short_solution(str)
end
```java
/* date - 23/09/2020
* author - @Shashwat Gupta (shashwatxdevelop)
*/
import java.util.Scanner;
public class StringReverseAndPalin {
public static void main(String[] args) {
String s,s1=""; int i, l;
char ch = 0;
Scanner sc= new Scanner (System.in);
s = sc.nextLine(); // Input the string
l = s.length(); // Taking the length of string
for(i=l-1; i>=0; i--) // For loop for the extraction of character from the string s
{
ch = s.charAt(i);
s1 = s1+ ch; // Storing the extracted character in new string s1
}
System.out.println(s1); // Printing the new reversed string s1
if (s.equals(s1)) // if block to check if the reversed string is palindrome or not
System.out.println("String is Palindrome");
else
System.out.println("String is not Palindrome");
}
}
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