Modify a sentence by reversing order of occurrences of all Palindrome Words

Given a string S representing a sentence, the task is to reverse the order of all palindromic words present in the sentence.

Examples:

Input: S = “mom and dad went to eye hospital”
Output: eye and dad went to mom hospital
Explanation: All palindromic words present in the string are “mom”, “dad” and “eye“, in the order of their occurrence. Reversing the order of their occurrence generates the sequence {“eye”, “dad”, “mom”}. Therefore, the modified string is “eye and dad went to mom hospital”.

Input : S = “wow it is next level”
Output: level it is next wow.

Approach: Follow the steps below to solve the problem:

• Iterate over the characters of the string S and split the space-separated words from the sentence using split() and store them in a list, say lis.
• Append all the palindromic words to a new list, say newlist, using append() function.
• Reverse this new list using reverse() function.
• Traverse the list lis and keep replacing the palindromic words with the newlist[i] ( initially, i=0 ) and increment i by 1.
• Print the modified sentence

Below is the implementation of the above approach:

Java

// Java implementation of
// the above approach
import java.util.*;

class GFG{

// Function to check if a
// string S is a palindrome
static boolean palindrome(String str)
{
    int st = 0;
    int ed = str.length() - 1;

    while (st < ed)
    {
        if (str.charAt(st) == str.charAt(ed))
        {
            st++;
            ed--;
        }
        else
            return false;
    }
    return true;
}

// Function to print the modified string
// after reversing the order of occurrences
// of all palindromic words in the sentence
static void printReverse(String sentence)
{

    // Stores the palindromic words
    ArrayList<String> newlist = new ArrayList<String>();
    ArrayList<String> lis = new ArrayList<String>();

    // Stores the words in the list
    String temp = "";

    for(char x: sentence.toCharArray())
    {
        if (x == ' ')
        {
            lis.add(temp);
            temp = "";
        }
        else
            temp += x;
    }
    lis.add(temp);

    // Traversing the list
    for(String x:  lis)
    {

        // If current word is a palindrome
        if (palindrome(x))

            // Update newlist
            newlist.add(x);
    }

    // Reverse the newlist
    Collections.reverse(newlist);

    int j = 0;

    // Traverse the list
    for(int i = 0; i < lis.size(); i++)
    {

        // If current word is a palindrome
        if (palindrome(lis.get(i)))
        {

            // Update lis[i]
            lis.set(i,newlist.get(j));

            // Increment j
            j = j + 1;
        }
    }

    // Print the updated sentence
    for(String x : lis)
        System.out.print(x + " ");
}

// Driver code
public static void main(String[] args)
{
    String sentence = "mom and dad went to eye hospital";
    printReverse(sentence);
}
}

// This code is contributed by offbeat

Python3

# Python implementation of
# the above approach

# Function to check if a
# string S is a palindrome
def palindrome(string):

    if(string == string[::-1]):
        return True
    else:
        return False

# Function to print the modified string
# after reversing the order of occurrences
# of all palindromic words in the sentence
def printReverse(sentence):

    # Stores the palindromic words
    newlist = []

    # Stores the words in the list
    lis = list(sentence.split())

    # Traversing the list
    for i in lis:

        # If current word is a palindrome
        if(palindrome(i)):

              # Update newlist
            newlist.append(i)

    # Reverse the newlist
    newlist.reverse()

    j = 0

    # Traverse the list
    for i in range(len(lis)):

        # If current word is a palindrome
        if(palindrome(lis[i])):

            # Update lis[i]
            lis[i] = newlist[j]

            # Increment j
            j = j + 1

    # Print the updated sentence
    for i in lis:
        print(i, end =" ")


# Driver Code

sentence = "mom and dad went to eye hospital"
printReverse(sentence)

C#

// C# implementation of
// the above approach
using System;
using System.Collections.Generic;

class GFG{

// Function to check if a
// string S is a palindrome
static bool palindrome(string str)
{
    int st = 0;
    int ed = str.Length - 1;

    while (st < ed)
    {
        if (str[st] == str[ed])
        {
            st++;
            ed--;
        }
        else
            return false;
    }
    return true;
}

// Function to print the modified string
// after reversing the order of occurrences
// of all palindromic words in the sentence
static void printReverse(string sentence)
{

    // Stores the palindromic words
    List<string> newlist = new List<string>();
    List<string> lis = new List<string>();

    // Stores the words in the list
    string temp = "";

    foreach(char x in sentence)
    {
        if (x == ' ')
        {
            lis.Add(temp);
            temp = "";
        }
        else
            temp += x;
    }
    lis.Add(temp);

    // Traversing the list
    foreach(string x in lis)
    {

        // If current word is a palindrome
        if (palindrome(x))

            // Update newlist
            newlist.Add(x);
    }

    // Reverse the newlist
    newlist.Reverse();

    int j = 0;

    // Traverse the list
    for(int i = 0; i < lis.Count; i++)
    {

        // If current word is a palindrome
        if (palindrome(lis[i]))
        {

            // Update lis[i]
            lis[i] = newlist[j];

            // Increment j
            j = j + 1;
        }
    }

    // Print the updated sentence
    foreach(string x in lis)
        Console.Write(x + " ");
}

// Driver Code
public static void Main()
{
    string sentence = "mom and dad went to eye hospital";
    printReverse(sentence);
}
}

// This code is contributed by ukasp

Javascript

<script>
// Javascript implementation of
// the above approach

// Function to check if a
// string S is a palindrome
function palindrome(str)
{
    var st = 0;
    var ed = str.length - 1;

    while (st < ed)
    {
        if (str[st] == str[ed])
        {
            st++;
            ed--;
        }
        else
          return false;
    }
    return true;
}

// Function to print the modified string
// after reversing the order of occurrences
// of all palindromic words in the sentence
function printReverse(sentence)
{

    // Stores the palindromic words
    var newlist = [];
    var lis = [];

    // Stores the words in the list
    var temp = "";

    for(var i =0; i<sentence.length;i++)
    {
        if (sentence[i] == ' ')
        {
            lis.push(temp);
            temp = "";
        }
        else
            temp += sentence[i];
    }
    lis.push(temp);

    // Traversing the list
    for(var i =0; i<lis.length;i++)
    {

        // If current word is a palindrome
        if (palindrome(lis[i]))

            // Update newlist
            newlist.push(lis[i]);
    }

    // Reverse the newlist
    newlist.reverse();

    var j = 0;

    // Traverse the list
    for(var i = 0; i < lis.length; i++)
    {

        // If current word is a palindrome
        if (palindrome(lis[i]))
        {

            // Update lis[i]
            lis[i] = newlist[j];

            // Increment j
            j = j + 1;
        }
    }

    // Print the updated sentence
    for(var i = 0; i < lis.length; i++)
    {
       document.write( lis[i] + " ");
    }
}

// Driver Code
var sentence = "mom and dad went to eye hospital";
printReverse(sentence);

</script>

C++

// C++ implementation of the above approach

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

// Function to check if a
// string S is a palindrome
bool palindrome(string str)
{
    int st = 0;
    int ed = str.length() - 1;

    while (st < ed)
    {
        if (str[st] == str[ed])
        {
            st++;
            ed--;
        }
        else
            return false;
    }
    return true;
}

// Function to print the modified string
// after reversing the order of occurrences
// of all palindromic words in the sentence
void printReverse(string sentence)
{

    // Stores the palindromic words
    vector<string> newlist;
    vector<string> lis;

    // Stores the words in the list
    string temp = "";

    for(char x: sentence)
    {
        if (x == ' ')
        {
            lis.push_back(temp);
            temp = "";
        }
        else
            temp += x;
    }
    lis.push_back(temp);

    // Traversing the list
    for(string x:  lis)
    {

        // If current word is a palindrome
        if (palindrome(x))

            // Update newlist
            newlist.push_back(x);
    }

    // Reverse the newlist
    reverse(newlist.begin(), newlist.end());

    int j = 0;

    // Traverse the list
    for(int i = 0; i < lis.size(); i++)
    {

        // If current word is a palindrome
        if (palindrome(lis[i]))
        {

            // Update lis[i]
            lis[i] = newlist[j];

            // Increment j
            j = j + 1;
        }
    }

    // Print the updated sentence
    for(string x : lis)
        cout << x << " ";
}

// Driver code
int main()
{
    string sentence = "mom and dad went to eye hospital";
    printReverse(sentence);
    return 0;
}

// Contributed by adityashae15

Output:

eye and dad went to mom hospital

Time Complexity: O(N)
Auxiliary Space: O(N) because it is using extra space for list newlist and lis