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Sort a string according to the order defined by another string

  • Difficulty Level : Easy
  • Last Updated : 11 Nov, 2021

Given two strings (of lowercase letters), a pattern, and a string. The task is to sort strings according to the order defined by the pattern. It may be assumed that the pattern has all characters of the string and all characters in the pattern appear only once.
Examples: 
 

Input  : pat = "bca", str = "abc"
Output : str = "bca"

Input  : pat = "bxyzca", str = "abcabcabc"
Output : str = "bbbcccaaa"

Input  : pat = "wcyuogmlrdfphitxjakqvzbnes", str = "jcdokai"
Output : str = "codijak"

 

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Approach 1:
The idea is to first count occurrences of all characters in str and store these counts in a count array. Then traverse pattern from left to right, and for each character pat[i], see how many times it appears in count array and copy this character these many times to str.
Below is the implementation of the above idea. 
 



Implementation:

C++




// C++ program to sort a string according to the
// order defined by a pattern string
#include <bits/stdc++.h>
using namespace std;
const int MAX_CHAR = 26;
 
// Sort str according to the order defined by pattern.
void sortByPattern(string& str, string pat)
{
    // Create a count array store count of characters in str.
    int count[MAX_CHAR] = { 0 };
 
    // Count number of occurrences of each character
    // in str.
    for (int i = 0; i < str.length(); i++)
        count[str[i] - 'a']++;
 
    // Traverse the pattern and print every characters
    // same number of times as it appears in str. This
    // loop takes O(m + n) time where m is length of
    // pattern and n is length of str.
    int index = 0;
    for (int i = 0; i < pat.length(); i++)
        for (int j = 0; j < count[pat[i] - 'a']; j++)
            str[index++] = pat[i];
}
 
// Driver code
int main()
{
    string pat = "bca";
    string str = "abc";
    sortByPattern(str, pat);
    cout << str;
    return 0;
}

Java




// Java program to sort a string according to the
// order defined by a pattern string
 
class GFG {
 
    static int MAX_CHAR = 26;
 
    // Sort str according to the order defined by pattern.
    static void sortByPattern(char[] str, char[] pat)
    {
        // Create a count array stor
        // count of characters in str.
        int count[] = new int[MAX_CHAR];
 
        // Count number of occurrences of
        // each character in str.
        for (int i = 0; i < str.length; i++) {
            count[str[i] - 'a']++;
        }
 
        // Traverse the pattern and print every characters
        // same number of times as it appears in str. This
        // loop takes O(m + n) time where m is length of
        // pattern and n is length of str.
        int index = 0;
        for (int i = 0; i < pat.length; i++) {
            for (int j = 0; j < count[pat[i] - 'a']; j++) {
                str[index++] = pat[i];
            }
        }
    }
 
    // Driver code
    public static void main(String args[])
    {
        char[] pat = "bca".toCharArray();
        char[] str = "abc".toCharArray();
        sortByPattern(str, pat);
        System.out.println(String.valueOf(str));
    }
}
 
// This code has been contributed by 29AjayKumar

Python3




# Python3 program to sort a string according to
# the order defined by a pattern string
MAX_CHAR = 26
 
# Sort str according to the order defined by pattern.
def sortByPattern(str, pat):
     
    global MAX_CHAR
     
    # Create a count array store count
    # of characters in str.
    count = [0] * MAX_CHAR
     
    # Count number of occurrences of
    # each character in str.
    for i in range (0, len(str)):
        count[ord(str[i]) - 97] += 1
     
    # Traverse the pattern and print every characters
    # same number of times as it appears in str. This
    # loop takes O(m + n) time where m is length of
    # pattern and n is length of str.
    index = 0;
    str = ""
     
    for i in range (0, len(pat)):
        j = 0
        while(j < count[ord(pat[i]) - ord('a')]):
            str += pat[i]
            j = j + 1
            index += 1
     
    return str
 
# Driver code
pat = "bca"
str = "abc"
print(sortByPattern(str, pat))
 
# This code is contributed by ihritik

C#




// C# program to sort a string according to the
// order defined by a pattern string
using System;
 
class GFG {
 
    static int MAX_CHAR = 26;
 
    // Sort str according to the order defined by pattern.
    static void sortByPattern(char[] str, char[] pat)
    {
        // Create a count array stor
        // count of characters in str.
        int[] count = new int[MAX_CHAR];
 
        // Count number of occurrences of
        // each character in str.
        for (int i = 0; i < str.Length; i++) {
            count[str[i] - 'a']++;
        }
 
        // Traverse the pattern and print every characters
        // same number of times as it appears in str. This
        // loop takes O(m + n) time where m is length of
        // pattern and n is length of str.
        int index = 0;
        for (int i = 0; i < pat.Length; i++) {
            for (int j = 0; j < count[pat[i] - 'a']; j++) {
                str[index++] = pat[i];
            }
        }
    }
 
    // Driver code
    public static void Main(String[] args)
    {
        char[] pat = "bca".ToCharArray();
        char[] str = "abc".ToCharArray();
        sortByPattern(str, pat);
        Console.WriteLine(String.Join("", str));
    }
}
 
/* This code contributed by PrinciRaj1992 */

Javascript




<script>
// Javascript program to sort a string according to the
// order defined by a pattern string
let MAX_CHAR = 26;
 
// Sort str according to the order defined by pattern.
function sortByPattern(str,pat)
{
    // Create a count array stor
        // count of characters in str.
        let count = new Array(MAX_CHAR);
        for(let i = 0; i < MAX_CHAR; i++)
        {
            count[i] = 0;
        }
   
        // Count number of occurrences of
        // each character in str.
        for (let i = 0; i < str.length; i++) {
            count[str[i].charCodeAt(0) - 'a'.charCodeAt(0)]++;
        }
   
        // Traverse the pattern and print every characters
        // same number of times as it appears in str. This
        // loop takes O(m + n) time where m is length of
        // pattern and n is length of str.
        let index = 0;
        for (let i = 0; i < pat.length; i++) {
            for (let j = 0; j < count[pat[i].charCodeAt(0) - 'a'.charCodeAt(0)]; j++) {
                str[index++] = pat[i];
            }
        }
}
 
// Driver code
let pat = "bca".split("");
let str = "abc".split("");
sortByPattern(str, pat);
document.write((str).join(""));
 
// This code is contributed by rag2127
</script>
Output
bca

Time complexity: O(m + n) where m is the length of the pattern and n is the length of str.
 

Approach 2: Using STL

We can pass a comparator to the sort() function in C++ and sort the string according to the pattern.

C++




#include <bits/stdc++.h>
using namespace std;
 
// Declaring a vector globally that stores which character
// is occuring first
vector<int> position(26, -1);
 
//Comparator function
bool cmp(char& char1, char& char2)
{
    return position[char1 - 'a'] < position[char2 - 'a'];
}
 
int main()
{
 
    // Pattern
    string pat = "wcyuogmlrdfphitxjakqvzbnes";
 
    for (int i = 0; i < pat.length(); i++) {
        if (position[pat[i] - 'a'] == -1)
            position[pat[i] - 'a'] = i;
    }
 
    // String to be sorted
    string str = "jcdokai";
 
    // Passing a comparator to sort function
    sort(str.begin(), str.end(), cmp);
    cout << str;
}
Output
codijak

Exercise: In the above solution, it is assumed that the pattern has all characters of str. Consider a modified version where the pattern may not have all characters and the task is to put all remaining characters (in the string but not in the pattern) at the end. The remaining characters need to be put in alphabetically sorted order.Hint: In the second loop, when increasing the index and putting the character in str, we can also decrease the count at that time. And finally, we traverse the count array to put the remaining characters in alphabetically sorted order.

This article is contributed by Sanjay Khadda. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 




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