Sort an array of strings based on the given order

Difficulty Level : Hard
Last Updated : 29 Jun, 2021

Given an array of strings words[] and the sequential order of alphabets, our task is to sort the array according to the order given. Assume that the dictionary and the words only contain lowercase alphabets.

Examples:

Input: words = {“hello”, “geeksforgeeks”}, order = “hlabcdefgijkmnopqrstuvwxyz”
Output: “hello”, “geeksforgeeks”
Explanation:
According to the given order ‘h’ occurs before ‘g’ and hence the words are considered to be sorted.
Input: words = {“word”, “world”, “row”}, order = “worldabcefghijkmnpqstuvxyz”
Output: “world”, “word”, “row”
Explanation:
According to the given order ‘l’ occurs before ‘d’ hence the words “world” will be kept first.

Approach: To solve the problem mentioned above we need to maintain the priority of each character in the given order. For doing that use Map Data Structure.

Iterate in the given order and set the priority of a character to its index value.
Use a custom comparator function to sort the array.
In the comparator function, iterate through the minimum sized word between the two words and try to find the first different character, the word with the lesser priority value character will be the smaller word.
If the words have the same prefix, then the word with a smaller size is the smaller word.

Below is the implementation of above approach:

C++

// C++ program to sort an array
// of strings based on the given order
 
#include <bits/stdc++.h>
using namespace std;
 
// For storing priority of each character
unordered_map<char, int> mp;
 
// Custom comparator function for sort
bool comp(string& a, string& b)
{
 
    // Loop through the minimum size
    // between two words
    for (int i = 0;
         i < min(a.size(), b.size());
         i++) {
 
        // Check if the characters
        // at position i are different,
        // then the word containing lower
        // valued character is smaller
        if (mp[a[i]] != mp[b[i]])
            return mp[a[i]] < mp[b[i]];
    }
 
    /* When loop breaks without returning, it
       means the prefix of both words were same
       till the execution of the loop.
       Now, the word with the smaller size will
       occur before in sorted order
        */
    return (a.size() < b.size());
}
 
// Function to print the
// new sorted array of strings
void printSorted(vector<string> words,
                 string order)
{
 
    // Mapping each character
    // to its occurrence position
    for (int i = 0; i < order.size(); i++)
        mp[order[i]] = i;
 
    // Sorting with custom sort function
    sort(words.begin(), words.end(), comp);
 
    // Printing the sorted order of words
    for (auto x : words)
        cout << x << " ";
}
 
// Driver code
int main()
{
 
    vector<string> words
        = { "word", "world", "row" };
    string order
        = { "worldabcefghijkmnpqstuvxyz" };
 
    printSorted(words, order);
 
    return 0;
}

Python3

# Python3 program to sort an array
# of strings based on the given order
from functools import cmp_to_key
 
# For storing priority of each character
mp = {}
 
# Custom comparator function for sort
def comp(a, b):
     
    # Loop through the minimum size
    # between two words
    for i in range( min(len(a), len(b))):
         
        # Check if the characters
        # at position i are different,
        # then the word containing lower
        # valued character is smaller
        if (mp[a[i]] != mp[b[i]]):
            if mp[a[i]] < mp[b[i]]:
                return -1
            else:
                return 1
     
    '''When loop breaks without returning, it
    means the prefix of both words were same
    till the execution of the loop.
    Now, the word with the smaller size will
    occur before in sorted order'''
    if (len(a) < len(b)):
        return -1
    else:
        return 1
 
# Function to print the
# new sorted array of strings
def printSorted(words, order):
     
    # Mapping each character
    # to its occurrence position
    for i in range(len(order)):
        mp[order[i]] = i
     
    # Sorting with custom sort function
    words = sorted(words, key = cmp_to_key(comp))
     
    # Printing the sorted order of words
    for x in words:
        print(x, end = " ")
 
# Driver code
words = [ "word", "world", "row" ]
order = "worldabcefghijkmnpqstuvxyz"
 
printSorted(words, order)
 
# This code is contributed by Shivani

Output:

world word row

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