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Print the arranged positions of characters to make palindrome in C Program.
You are provided with a string str with some length n. Print the position of every element of the string so it can form a palindrome, else print a message “No palindrome” on screen.
What is palindrome?
Palindrome is a word, sequence of characters which reads same from the reverse or backward as from the forward manner, like MADAM, racecar.
To find a sequence or a word is palindrome we generally store the reverse of a word in a separate string and compare both if they are same then the given word or sequence is palindrome. But in this question we have to print the arrangement to make a word or a sequence in palindrome.
Like, there is a string str = “tinni” then it can be intni or nitin so we have to return any one of the sequence of arrangement as index starting from 1 and result can be either 2 3 1 4 5 or 3 2 1 5 4 of the two.
The above problem needs a solution like the given example below −
Example
Input: string str = “baa” Output: 2 1 3 Input: string str = “tinni” Output: 2 3 1 4 5
Algorithm
void printPalindromePos(string &str) START STEP 1: DECLARE vector<int> pos[MAX] STEP 2: DECLARE AND ASSIGN n WITH LENGTH OF str STEP 3: LOOP FOR i = 0 AND i < n AND i++ pos[str[i]].push_back(i+1) END LOOP STEP 4: SET oddCount = 0 STEP 5: DECLARE oddChar STEP 6: LOOP FOR i=0 AND i<MAX AND i++ IF pos[i].size() % 2 != 0 THEN, INCREMENT oddCount BY 1 SET oddChar AS i END IF END FOR STEP 7: IF oddCount > 1 THEN, PRINT "NO PALINDROME" STEP 8: LOOP FOR i=0 AND i<MAX AND i++ DECRLARE mid = pos[i].size()/2 LOOP FOR j=0 AND j<mid AND j++ PRINT pos[i][j] END LOOP END LOOP STEP 9: IF oddCount > 0 THEN, DECLARE AND SET last = pos[oddChar].size() - 1 PRINT pos[oddChar][last] SET pos[oddChar].pop_back(); END IF STEP 10: LOOP FOR i=MAX-1 AND i>=0 AND i-- DECLARE AND SET count = pos[i].size() LOOP FOR j=count/2 AND j<count AND j++ PRINT pos[i][j] STOP
Example
#include <bits/stdc++.h>
using namespace std;
// Giving the maximum characters
const int MAX = 256;
void printPalindromePos(string &str){
//Inserting all positions of characters in the given string.
vector<int> pos[MAX];
int n = str.length();
for (int i = 0; i < n; i++)
pos[str[i]].push_back(i+1);
/* find the number of odd elements.Takes O(n) */
int oddCount = 0;
char oddChar;
for (int i=0; i<MAX; i++) {
if (pos[i].size() % 2 != 0) {
oddCount++;
oddChar = i;
}
}
/* Palindrome can't contain more than 1 odd characters */
if (oddCount > 1)
cout << "NO PALINDROME";
/* Print positions in first half of palindrome */
for (int i=0; i<MAX; i++){
int mid = pos[i].size()/2;
for (int j=0; j<mid; j++)
cout << pos[i][j] << " ";
}
// Consider one instance odd character
if (oddCount > 0){
int last = pos[oddChar].size() - 1;
cout << pos[oddChar][last] << " ";
pos[oddChar].pop_back();
}
/* Print positions in second half of palindrome */
for (int i=MAX-1; i>=0; i--){
int count = pos[i].size();
for (int j=count/2; j<count; j++)
cout << pos[i][j] << " ";
}
}
int main(){
string s = "tinni";
printPalindromePos(s);
return 0;
}Output
If we run above program then it will generate following output −
2 3 1 4 5
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