# Rearrange characters to form palindrome if possible in C++

We are given with a string ‘str’ of any given length. The task is to rearrange the characters in such a manner that the output will be a palindrome string without adding or removing a character from the given input string. Palindrome string is the one in which the characters are arranged in such a manner that they pronounce the same from start and last.

## Let us see various input output scenarios for this −

Input − string str = "itnin"

Output − Rearrangement of characters to form palindrome if possible is: nitin

Explanation − We are given a string type variable let’s say, str. Now we will rearrange the characters of an input string in such a manner that it will be a palindrome string and if it’s not possible then it will return ‘NOT POSSIBLE’. So the output with the given input string is ‘nitin’.

Input − string str = "baaaba"

Output − Rearrangement of characters to form palindrome if possible is: aabbaa

Explanation − We are given a string type variable let’s say, str. Now we will rearrange the characters of an input string in such a manner that it will be a palindrome string and if it’s not possible then it will return ‘NOT POSSIBLE’. So the output with the given input string is ‘aabbaa’.

## Approach used in the below program is as follows

• Input a variable of string type, let’s say, str and calculate the size of a string and store it in a length named variable.

• Pass the data to the function Rearrangement(str, length).

• Inside the function Rearrangement(arr, length)

• Create a variable as ‘um’ of type unordered_map that is storing char and integer type pairs.

• Declare an integer type variable as total and set it with 0.

• Create a character type variable as ‘ch’ and string type variables as str_1 and str_2.

• Start loop FOR from i to 0 till i is less than length. Inside the loop, set um[str[i]] by an incremental value of 1.

• Start loop FOR to iterate map ‘um’. Inside the loop, check IF it.second % 2 not equals to 0 then increment the total by 1 and set ch with it.first.

• Check IF total greater than 1 OR total = 1 AND length % 2 = 0 then return 0.

• Start loop FOR to iterate map ‘um’. Inside the loop, set str(it.second / 2, it.first), str_1 to str_1 + str and str_2 to str + str_2.

• Check IF total = 1 then return str_1 + ch + str_2. ELSE, return str_1 + str_2.

• Print the result.

## Example

#include <bits/stdc++.h>
using namespace std;
string Rearrangement(string str, int length){
unordered_map<char, int> um;
int total = 0;
char ch;
string str_1 = "";
string str_2 = "";

for (int i = 0; i < length; i++){
um[str[i]]++;
}
for(auto it : um){
if(it.second % 2 != 0){
total++;
ch = it.first;
}
}
if(total > 1 || total == 1 && length % 2 == 0){
return 0;
}
for(auto it : um){
string str(it.second / 2, it.first);
str_1 = str_1 + str;
str_2 = str + str_2;
}
if(total == 1){
return str_1 + ch + str_2;
}
else{
return str_1 + str_2;
}
}
int main(){
string str = "itnin";
int length = str.size();
cout<<"Rearrangement of characters to form palindrome if possible is: "<<Rearrangement(str, length);
return 0;
}

## Output

If we run the above code it will generate the following Output

Rearrangement of characters to form palindrome if possible is: nitin