Construct lexicographically smallest palindrome
Given a string of lowercase alphabets. Some of characters of given string got corrupted and are now represented by *. We can replace * with any of lowercase alphabets. You have to construct lexicographically smallest palindrome string. If it is not possible to construct a palindrome print “Not Possible”.
Examples:
Input : str[] = "bc*b" Output : bccb Input : str[] = "bc*a*cb" Output : bcaaacb Input : str[] = "bac*cb" Output : Not Possible
Start traversing the string from both end. Say with i=0, j=strlen-1, keep increasing i and decreasing j after every single iteration till i exceeds j. Now at any intermediate position we have five possible case :
- str[i] and str[j] both are same and also not equal to ‘*’. In this case simply continue.
- str[i] and str[j] both are same and are equal to ‘*’. Here you must fill str[i] = str[j] = ‘a’ for smallest possible palindrome.
- str[i] equals to ‘*’ and str[j] is some alphabet. Here fill str[i] = str[j] to make our string a palindrome.
- str[j] equals to ‘*’ and str[i] is some alphabet. Here fill str[j] = str[i] to make our string a palindrome.
- str[i] is not equals to str[j] and also both are some alphabet. In this case palindrome construction is not possible. So, print “Not Possible” and break from loop.
After i exceeds j means we have got our required palindrome. Else we got “Not possible” as result.
C++
// CPP for constructing smallest palindrome #include <bits/stdc++.h> using namespace std; // function for printing palindrome string constructPalin(string str, int len) { int i = 0, j = len - 1; // iterate till i<j for (; i < j; i++, j--) { // continue if str[i]==str[j] if (str[i] == str[j] && str[i] != '*') continue; // update str[i]=str[j]='a' if both are '*' else if (str[i] == str[j] && str[i] == '*') { str[i] = 'a'; str[j] = 'a'; continue; } // update str[i]=str[j] if only str[i]='*' else if (str[i] == '*') { str[i] = str[j]; continue; } // update str[j]=str[i] if only str[j]='*' else if (str[j] == '*') { str[j] = str[i]; continue; } // else print not possible and return cout << "Not Possible"; return ""; } return str; } // driver program int main() { string str = "bca*xc**b"; int len = str.size(); cout << constructPalin(str, len); return 0; } |
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Java
// Java for constructing smallest palindrome class GFG { // function for printing palindrome static String constructPalin(char []str, int len) { int i = 0, j = len - 1; // iterate till i<j for (; i < j; i++, j--) { // continue if str[i]==str[j] if (str[i] == str[j] && str[i] != '*') continue; // update str[i]=str[j]='a' if both are '*' else if (str[i] == str[j] && str[i] == '*') { str[i] = 'a'; str[j] = 'a'; continue; } // update str[i]=str[j] if only str[i]='*' else if (str[i] == '*') { str[i] = str[j]; continue; } // update str[j]=str[i] if only str[j]='*' else if (str[j] == '*') { str[j] = str[i]; continue; } // else print not possible and return System.out.println("Not Possible"); return ""; } return String.valueOf(str); } // Driver code public static void main(String[] args) { String str = "bca*xc**b"; int len = str.length(); System.out.println(constructPalin(str.toCharArray(), len)); } } // This code is contributed by 29AjayKumar |
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Python3
# Python3 for constructing smallest palindrome # function for printing palindrome def constructPalin(string, l): string = list(string) i = -1 j = l # iterate till i<j while i < j: i += 1 j -= 1 # continue if str[i]==str[j] if (string[i] == string[j] and string[i] != '*'): continue # update str[i]=str[j]='a' if both are '*' elif (string[i] == string[j] and string[i] == '*'): string[i] = 'a' string[j] = 'a' continue # update str[i]=str[j] if only str[i]='*' elif string[i] == '*': string[i] = string[j] continue # update str[j]=str[i] if only str[j]='*' elif string[j] == '*': string[j] = string[i] continue # else print not possible and return print("Not Possible") return "" return ''.join(string) # Driver Code if __name__ == "__main__": string = "bca*xc**b" l = len(string) print(constructPalin(string, l)) # This code is contributed by # sanjeev2552 |
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C#
// C# for constructing smallest palindrome using System; class GFG { // function for printing palindrome static String constructPalin(char []str, int len) { int i = 0, j = len - 1; // iterate till i<j for (; i < j; i++, j--) { // continue if str[i]==str[j] if (str[i] == str[j] && str[i] != '*') continue; // update str[i]=str[j]='a' if both are '*' else if (str[i] == str[j] && str[i] == '*') { str[i] = 'a'; str[j] = 'a'; continue; } // update str[i]=str[j] if only str[i]='*' else if (str[i] == '*') { str[i] = str[j]; continue; } // update str[j]=str[i] if only str[j]='*' else if (str[j] == '*') { str[j] = str[i]; continue; } // else print not possible and return Console.WriteLine("Not Possible"); return ""; } return String.Join("",str); } // Driver code public static void Main(String[] args) { String str = "bca*xc**b"; int len = str.Length; Console.WriteLine(constructPalin(str.ToCharArray(), len)); } } // This code contributed by Rajput-Ji |
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PHP
<?php // PHP for constructing smallest palindrome // function for printing palindrome function constructPalin($str, $len) { $i = 0; $j = $len - 1; // iterate till i<j for (; $i < $j; $i++, $j--) { // continue if str[i]==str[j] if ($str[$i] == $str[$j] && $str[$i] != '*') continue; // update str[i]=str[j]='a' if both are '*' else if ($str[$i] == $str[$j] && $str[$i] == '*') { $str[$i] = 'a'; $str[$j] = 'a'; continue; } // update str[i]=str[j] if only str[i]='*' else if ($str[$i] == '*') { $str[$i] = $str[$j]; continue; } // update str[j]=str[i] if only str[j]='*' else if ($str[$j] == '*') { $str[$j] = $str[$i]; continue; } // else print not possible and return echo "Not Possible"; return ""; } return $str; } // Driver Code $str = "bca*xc**b"; $len = strlen($str); echo constructPalin($str, $len); // This code is contributed by ita_c ?> |
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Output:
bcacxcacb
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