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Shortest substring of a string containing all given words

  • Difficulty Level : Hard
  • Last Updated : 01 Apr, 2019

Print the shortest sub-string of a string containing all the given words.

In the first example, two solutions are possible: “world is here. this is a life full of ups” and “ups and downs. life is world”.

  1. Initialize HashMap with all the given words which are required to be searched and assign their values as -1.
  2. Maintain a counter.
  3. Traverse the entire String word by word and do following for each sentence word
    • If the sentence word exists in the list of words you’re looking for, update the last position of that word.
    • Increase the total count if the updated last position was not initialized.
    • If the total count is equal to count of all given words, loop through the last positions and find the smallest one. The distance between the current position and that value will be the length of the substring. Record these values and find the best one over all positions

Below is Java implementation of above steps.




// Java program to find the shortest substring of a
// string containing all given words using HashMap
import java.io.*;
import java.util.*;
import java.util.HashMap;
  
class Shortest {
  
    public static void findShortest(String sentence,
                                     String[] words)
    {
        // Make an array of words from given sentence
        // We remove punctuations before splitting.
        String replicate = sentence.replace(".", "");
        replicate = replicate.replace(", ", "");
        replicate = replicate.replace("!", "");
        String sent_words[] = replicate.split(" ");
  
        // hashmap to store given words in a map.
        HashMap<String, Integer> map = new HashMap<>();
        int length = words.length;
        for (int i = 0; i < length; i++)
            map.put(words[i], -1);
  
        // Traverse through all sentence words
        // and if they match with given words
        // then mark their appearances in map.
        int len_sub = Integer.MAX_VALUE;
        int count = 0;
        int local_start = 0, local_end = 0;
        for (int i = 0; i < sent_words.length; i++) {
            if (map.containsKey(sent_words[i]) == true) {
  
                // If this is the first occurrence
                int index = map.get(sent_words[i]);
                if (index == -1)
                    count++;
  
                // Store latest index
                map.put(sent_words[i], i);
  
                // If all words matched
                if (count == length) {
  
                    // Find smallest index
                    int min = Integer.MAX_VALUE;
                    for (Map.Entry<String, Integer> m :
                                     map.entrySet()) {
                        int val = m.getValue();
                        if (val < min)
                            min = val;
                    }
  
                    // Check if current length is smaller
                    // then length so far
                    int s = i - min;
                    if (s < len_sub) {
                        local_start = min;
                        local_end = i;
                        len_sub=s;
                    }
                }
            }
        }
  
        // Printing original substring (with punctuations)
        // using resultant local_start and local_end.
        String[] original_parts = sentence.split(" ");
        for (int i = local_start; i <=local_end; i++)
            System.out.print(original_parts[i] + " ");
    }
  
    // Driver code
    public static void main(String args[])
    {
        String sentence = "The world is here. this is a" +
            " life full of ups and downs. life is world.";
        String[] words = { "life", "ups", "is", "world" };
        findShortest(sentence, words);
    }
}

Output :



ups and downs. life is 

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