Smallest substring occurring only once in a given string

Given a string S consisting of N lowercase alphabets, the task is to find the length of the smallest substring in S whose occurrence is exactly 1.

Examples:

Input: S = “abaaba”
Output: 2
Explanation: 
The smallest substring in the string S, whose occurrence is exactly 1 is “aa” . Length of this substring is 2.
Therefore, print 2.

Input: S = “zyzyzyz”
Output: 5

Approach: To solve the problem, the idea is to generate all possible substring of the given string S and store the frequency of each substring in a HashMap. Now, traverse the HashMap and print the substring of minimum length whose frequency is 1. 

Below is the implementation of the above approach:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to find the smallest
// substring occurring only once
int smallestSubstring(string a)
{

    // Stores all occurrences
    vector<string> subStrings;
    int n = a.size();
    // Generate all the substrings
    for (int i = 0; i < n; i++)
        for (int len = 1; len <= n - i; len++)
            subStrings.push_back(a.substr(i, len));

    // Take into account
    // all the substrings
    map<string,int> subStringsFreq;
    for(string i: subStrings) {
        subStringsFreq[i]++;
    }

    // Iterate over all
    // unique substrings
    int ans = INT_MAX;
    for (auto str : subStringsFreq)
    {
        if (str.second == 1){
            //Find minimum length of substring
            int str_len = str.first.size();
            ans = min(ans, str_len);
        }
    }

      // return 0 if no such substring exists
    return ans == INT_MAX ? 0 : ans;
}

// Driver Code
int main()
{
  string S = "ababaabba";
  cout<<smallestSubstring(S);
  return 0;
}

// This code is contributed by mohit kumar 29.

Java

// Java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;

class GFG{

// Function to find the smallest
// substring occurring only once
static int smallestSubstring(String a)
{

    // Stores all occurrences
    ArrayList<String> a1 = new ArrayList<>();

    // Generate all the substrings
    for(int i = 0; i < a.length(); i++)
    {
        for(int j = i + 1; j <= a.length(); j++)
        {

            // Avoid multiple occurences
            if (i != j)

                // Append all substrings
                a1.add(a.substring(i, j));
        }
    }

    // Take into account
    // all the substrings
    TreeMap<String, Integer> a2 = new TreeMap<>();
    for(String s : a1)
        a2.put(s, a2.getOrDefault(s, 0) + 1);

    ArrayList<String> freshlist = new ArrayList<>();

    // Iterate over all
    // unique substrings
    for(String s : a2.keySet())
    {

        // If frequency is 1
        if (a2.get(s) == 1)

            // Append into fresh list
            freshlist.add(s);
    }

    // Initialize a dictionary
    TreeMap<String, Integer> dictionary = new TreeMap<>();

    for(String s : freshlist)
    {

        // Append the keys
        dictionary.put(s, s.length());
    }

    ArrayList<Integer> newlist = new ArrayList<>();

    // Traverse the dictionary
    for(String s : dictionary.keySet())
        newlist.add(dictionary.get(s));

    int ans = Integer.MAX_VALUE;

    for(int i : newlist)
        ans = Math.min(ans, i);

    // Return the minimum of dictionary
    return ans == Integer.MAX_VALUE ? 0 : ans;
}

// Driver Code
public static void main(String[] args)
{
    String S = "ababaabba";

    System.out.println(smallestSubstring(S));
}
}

// This code is contributed by Kingash

Python3

# Python3 program of the above approach
from collections import Counter

# Function to find the smallest
# substring occurring only once
def smallestSubstring(a):

    # Stores all occurrences
    a1 = []

    # Generate all the substrings
    for i in range(len(a)):
        for j in range(i+1, len(a)):

            # Avoid multiple occurrences
            if i != j:

                # Append all substrings
                a1.append(a[i:j+1])

    # Take into account
    # all the substrings
    a2 = Counter(a1)
    freshlist = []

    # Iterate over all
    # unique substrings
    for i in a2:

          # If frequency is 1
        if a2[i] == 1:

            # Append into fresh list
            freshlist.append(i)

    # Initialize a dictionary
    dictionary = dict()

    for i in range(len(freshlist)):

        # Append the keys
        dictionary[freshlist[i]] = len(freshlist[i])

    newlist = []

    # Traverse the dictionary
    for i in dictionary:
        newlist.append(dictionary[i])

    # Print the minimum of dictionary
    return(min(newlist))

# Driver Code
S = "ababaabba"
print(smallestSubstring(S))

C#

using System;
using System.Collections.Generic;
using System.Linq;

class GFG
{
  // Function to find the smallest
  // substring occurring only once
  static int SmallestSubstring(string a)
  {
    // Stores all occurrences
    var a1 = new List<string>();

    // Generate all the substrings
    for (int i = 0; i < a.Length; i++)
    {
      for (int j = i + 1; j <= a.Length; j++)
      {
        // Avoid multiple occurences
        if (i != j)

          // Append all substrings
          a1.Add(a.Substring(i, j - i));
      }
    }

    // Take into account
    // all the substrings
    var a2 = new Dictionary<string, int>();
    foreach (string s in a1)
      if (a2.ContainsKey(s))
        a2[s]++;
    else
      a2[s] = 1;

    var freshlist = new List<string>();

    // Iterate over all
    // unique substrings
    foreach (string s in a2.Keys)
    {
      // If frequency is 1
      if (a2[s] == 1)

        // Append into fresh list
        freshlist.Add(s);
    }

    // Initialize a dictionary
    var dictionary = new Dictionary<string, int>();

    foreach (string s in freshlist)
    {
      // Append the keys
      dictionary[s] = s.Length;
    }

    var newlist = new List<int>();

    // Traverse the dictionary
    foreach (string s in dictionary.Keys)
      newlist.Add(dictionary[s]);

    int ans = int.MaxValue;

    foreach (int i in newlist)
      ans = Math.Min(ans, i);

    // Return the minimum of dictionary
    return ans == int.MaxValue ? 0 : ans;
  }

  // Driver Code
  static void Main(string[] args)
  {
    string S = "ababaabba";

    Console.WriteLine(SmallestSubstring(S));
  }
}


// This code is contributed by phasing17

Javascript

<script>

// JavaScript program for the above approach

// Function to find the smallest
// substring occurring only once
function smallestSubstring(a)
{
    // Stores all occurrences
    let a1 = [];

    // Generate all the substrings
    for(let i = 0; i < a.length; i++)
    {
        for(let j = i + 1; j <= a.length; j++)
        {

            // Avoid multiple occurrences
            if (i != j)

                // Append all substrings
                a1.push(a.substring(i, j));
        }
    }

    // Take into account
    // all the substrings
    let a2 = new Map();
    for(let s=0;s<a1.length;s++)
    {
        if(a2.has(a1[s]))
            a2.set(a1[s],a2.get(a1[s])+1);
        else
            a2.set(a1[s],1);
    }

    let freshlist = [];

    // Iterate over all
    // unique substrings
    for(let s of a2.keys())
    {

        // If frequency is 1
        if (a2.get(s) == 1)

            // Append into fresh list
            freshlist.push(s);
    }

    // Initialize a dictionary
    let dictionary = new Map();

    for(let s=0;s<freshlist.length;s++)
    {
        // Append the keys
        dictionary.set(freshlist[s],
        freshlist[s].length);
    }


    let newlist = [];

    // Traverse the dictionary
    for(let s of dictionary.keys())
        newlist.push(dictionary.get(s));

    let ans = Number.MAX_VALUE;

    for(let i=0;i<newlist.length;i++)
        ans = Math.min(ans, newlist[i]);

    // Return the minimum of dictionary
    return ans == Number.MAX_VALUE ? 0 : ans;
}

// Driver Code
let S = "ababaabba";
document.write(smallestSubstring(S));



// This code is contributed by unknown2108

</script>

Output:

2

Time Complexity: O(N²)
Auxiliary Space: O(N²)