Sub-string that contains all lowercase alphabets after performing the given operation

Given a string str containing lower case alphabets and character ‘?’. The task is to check if it is possible to make str good or not.

A string is called good if it contains a sub-string of length 26 which has every character of lower case alphabets in it.

The task is to check if it is possible to make the string good by replacing ‘?’ characters with any lower case alphabet. If it is possible then print the modified string otherwise print -1.

Examples:

Input: str = “abcdefghijkl?nopqrstuvwxy?”
Output: abcdefghijklmnopqrstuvwxyz
Replace first ‘?’ with ‘m’ and second with ‘z’.

Input: str = “abcdefghijklmnopqrstuvwxyz??????”
Output: abcdefghijklmnopqrstuvwxyzaaaaaa
Given string already has a sub-string which contains all the 26 lower case alphabets.



Approach: If the length of the string is less than 26 then print -1. The Task is to make a sub-string of length 26 that has all the lowercase characters. Thus, the simplest way is to iterate through all sub-strings of length 26 then for each sub-string count the number of occurrences of each alphabet, ignoring the question marks. After that, if there exists a character that occurs twice or more then this sub-string cannot contain all letters of the alphabet, and we process the next sub-string. Otherwise, we can fill in the question marks with the letters that have not appeared in the sub-string and obtain a sub-string of length 26 which contains all letters of the alphabet.

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function that returns true if every
// lowercase character appears atmost once
bool valid(int cnt[])
{
    // every character frequency must be not
    // greater than one
    for (int i = 0; i < 26; i++) {
        if (cnt[i] >= 2)
            return false;
    }
  
    return true;
}
  
// Function that returns the modified 
// good string if possible
string getGoodString(string s, int n)
{
    // If the length of the string is less than n
    if (n < 26)
        return "-1";
  
    // Sub-strings of length 26
    for (int i = 25; i < n; i++) {
  
        // To store frequency of each character
        int cnt[26] = { 0 };
  
        // Get the frequency of each character 
        // in the current sub-string
        for (int j = i; j >= i - 25; j--) {
            cnt[s[j] - 'a']++;
        }
  
        // Check if we can get sub-string containing all
        // the 26 characters
        if (valid(cnt)) {
  
            // Find which character is missing
            int cur = 0;
            while (cnt[cur] > 0)
                cur++;
  
            for (int j = i - 25; j <= i; j++) {
  
                // Fill with missing characters
                if (s[j] == '?') {
                    s[j] = cur + 'a';
                    cur++;
  
                    // Find the next missing character
                    while (cnt[cur] > 0)
                        cur++;
                }
            }
  
            // Return the modified good string
            return s;
        }
    }
  
    return "-1";
}
  
// Driver code
int main()
{
    string s = "abcdefghijkl?nopqrstuvwxy?";
    int n = s.length();
  
    cout << getGoodString(s, n);
  
    return 0;
}

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Java

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// Java implementation of the approach
import java.util.*;
  
class GFG
{
      
// Function that returns true if every
// lowercase character appears atmost once
static boolean valid(int []cnt)
{
    // every character frequency must be not
    // greater than one
    for (int i = 0; i < 26; i++)
    {
        if (cnt[i] >= 2)
            return false;
    }
  
    return true;
}
  
// Function that returns the modified 
// good string if possible
static String getGoodString(String ss, int n)
{
    char[] s=ss.toCharArray();
      
    // If the length of the string is less than n
    if (n < 26)
        return "-1";
          
    // To store frequency of each character
        int[] cnt = new int[27];
          
    // Sub-strings of length 26
    for (int i = 25; i < n; i++) 
    {
  
          
  
        // Get the frequency of each character 
        // in the current sub-string
        for (int j = i; j >= i - 25; j--) 
        {
            if (s[j] != '?')
            cnt[((int)s[j] - (int)'a')]++;
        }
  
        // Check if we can get sub-string containing all
        // the 26 characters
        if (valid(cnt))
        {
  
            // Find which character is missing
            int cur = 0;
            while (cnt[cur] > 0)
                cur++;
  
            for (int j = i - 25; j <= i; j++) 
            {
  
                // Fill with missing characters
                if (s[j] == '?'
                {
                    s[j] = (char)(cur + (int)('a'));
                    cur++;
  
                    // Find the next missing character
                    while (cnt[cur] > 0)
                        cur++;
                }
            }
  
            // Return the modified good string
            return new String(s);
        }
    }
  
    return "-1";
}
  
// Driver code
public static void main (String[] args)
{
    String s = "abcdefghijkl?nopqrstuvwxy?";
    int n = s.length();
  
    System.out.println(getGoodString(s, n));
}
}
  
// This code is contributed by chandan_jnu

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Python3

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# Python3 implementation of the approach 
  
# Function that returns true if every 
# lowercase character appears atmost once 
def valid(cnt): 
  
    # Every character frequency must 
    # be not greater than one 
    for i in range(0, 26): 
        if cnt[i] >= 2
            return False
  
    return True
  
# Function that returns the modified 
# good string if possible 
def getGoodString(s, n): 
  
    # If the length of the string is
    # less than n 
    if n < 26:
        return "-1"
  
    # Sub-strings of length 26 
    for i in range(25, n): 
  
        # To store frequency of each character 
        cnt = [0] * 26
  
        # Get the frequency of each character 
        # in the current sub-string 
        for j in range(i, i - 26, -1): 
            if s[j] != '?':
                cnt[ord(s[j]) - ord('a')] += 1
  
        # Check if we can get sub-string 
        # containing the 26 characters all
        if valid(cnt): 
  
            # Find which character is missing 
            cur = 0
            while cur < 26 and cnt[cur] > 0
                cur += 1
  
            for j in range(i - 25, i + 1): 
  
                # Fill with missing characters 
                if s[j] == '?':
                    s[j] = chr(cur + ord('a')) 
                    cur += 1
  
                    # Find the next missing character 
                    while cur < 26 and cnt[cur] > 0:
                        cur += 1
  
            # Return the modified good string 
            return ''.join(s) 
  
    return "-1"
  
# Driver code 
if __name__ == "__main__":
  
    s = "abcdefghijkl?nopqrstuvwxy?"
    n = len(s) 
  
    print(getGoodString(list(s), n)) 
  
# This code is contributed by Rituraj Jain

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C#

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// C# implementation of the approach
using System;
  
class GFG
{
      
// Function that returns true if every
// lowercase character appears atmost once
static bool valid(int []cnt)
{
    // every character frequency must be not
    // greater than one
    for (int i = 0; i < 26; i++)
    {
        if (cnt[i] >= 2)
            return false;
    }
  
    return true;
}
  
// Function that returns the modified 
// good string if possible
static string getGoodString(string ss, int n)
{
    char[] s = ss.ToCharArray();
      
    // If the length of the string is less than n
    if (n < 26)
        return "-1";
          
    // To store frequency of each character
        int[] cnt = new int[27];
          
    // Sub-strings of length 26
    for (int i = 25; i < n; i++) 
    {
  
          
  
        // Get the frequency of each character 
        // in the current sub-string
        for (int j = i; j >= i - 25; j--) 
        {
            if (s[j] != '?')
            cnt[((int)s[j] - (int)'a')]++;
        }
  
        // Check if we can get sub-string containing all
        // the 26 characters
        if (valid(cnt))
        {
  
            // Find which character is missing
            int cur = 0;
            while (cnt[cur] > 0)
                cur++;
  
            for (int j = i - 25; j <= i; j++) 
            {
  
                // Fill with missing characters
                if (s[j] == '?'
                {
                    s[j] = (char)(cur + (int)('a'));
                    cur++;
  
                    // Find the next missing character
                    while (cnt[cur] > 0)
                        cur++;
                }
            }
  
            // Return the modified good string
            return new String(s);
        }
    }
  
    return "-1";
}
  
// Driver code
static void Main()
{
    string s = "abcdefghijkl?nopqrstuvwxy?";
    int n = s.Length;
  
    Console.WriteLine(getGoodString(s, n));
}
}
  
// This code is contributed by chandan_jnu

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PHP

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<?php 
// PHP implementation of the approach
  
// Function that returns true if every
// lowercase character appears atmost once
function valid(&$cnt)
{
    // every character frequency must 
    // be not greater than one
    for ($i = 0; $i < 26; $i++)
    {
        if ($cnt[$i] >= 2)
            return false;
    }
  
    return true;
}
  
// Function that returns the modified 
// good string if possible
function getGoodString($s, $n)
{
    // If the length of the string is 
    // less than n
    if ($n < 26)
        return "-1";
  
    // Sub-strings of length 26
    for ($i = 25; $i < $n; $i++) 
    {
  
        // To store frequency of each character
        $cnt = array_fill(0, 26, NULL); 
  
        // Get the frequency of each character 
        // in the current sub-string
        for ($j = $i; $j >= $i - 25; $j--) 
        {
            if ($s[$j] != '?')
            $cnt[ord($s[$j]) - ord('a')]++;
        }
  
        // Check if we can get sub-string 
        // containing all the 26 characters
        if (valid($cnt)) 
        {
  
            // Find which character is missing
            $cur = 0;
            while ($cur < 26 && $cnt[$cur] > 0)
                $cur++;
  
            for ($j = $i - 25; $j <= $i; $j++) 
            {
  
                // Fill with missing characters
                if ($s[$j] == '?')
                {
                    $s[$j] = chr($cur + ord('a'));
                    $cur++;
  
                    // Find the next missing character
                    while ($cur < 26 && $cnt[$cur] > 0)
                        $cur++;
                }
            }
  
            // Return the modified good string
            return $s;
        }
    }
  
    return "-1";
}
  
// Driver code
$s = "abcdefghijkl?nopqrstuvwxy?";
$n = strlen($s);
echo getGoodString($s, $n);
  
// This code is contributed by ita_c
?>

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Output:

abcdefghijklmnopqrstuvwxyz


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