Longest string which is prefix string of at least two strings

Given a set of strings of the same length, we need to find the length of the longest string, which is a prefix string of at least two strings.

Examples:

Input:  ["abcde", "abcsd", "bcsdf", "abcda", "abced"]
Output: 4
Explanation:  
Longest prefix string is "abcd".

Input:  ["pqrstq", "pwxyza", "abcdef", "pqrstu"]
Output: 5

Approach:

• Starting from the 0th position, iterate over every character and check if that character occurs in at least two of the strings at the current position or not.
• If it occurs, then recursively call on the next position. Otherwise,
• Update the max value by taking the current maximum with Current_position – 1.
• Finally, return the max value.

C++

// C++ program to find longest
// string which is prefix string
// of at least two strings
#include<bits/stdc++.h>
using namespace std;
int max1=0;

// Function to find Max length
// of the prefix
int MaxLength(vector<string> v, int i,
                                int m)
{
    // Base case
    if(i>=m)
    {
        return m-1;
    }

    // Iterating over all the alphabets
    for(int k = 0; k < 26; k++)
    {
        char c = 'a' + k;
        vector<string> v1;

        // Checking if char exists in
        // current string or not
        for(int j = 0; j < v.size(); j++)
        {
            if(v[j][i] == c)
            {
                v1.push_back(v[j]);
            }
        }

        // If atleast 2 string have
        // that character
        if(v1.size()>=2)
        {
           // Recursive call to i+1
           max1=max(max1,
                    MaxLength(v1, i+1, m));
        }
        else
        {
            max1=max(max1, i - 1);
        }
    }
    return max1;
}

// Driver code
int main()
{
  // Initialising strings
  string s1, s2, s3, s4, s5;

  s1 = "abcde";
  s2 = "abcsd";
  s3 = "bcsdf";
  s4 = "abcda";
  s5 = "abced";

  vector<string> v;

  // push strings into vectors.
  v.push_back(s1);
  v.push_back(s2);
  v.push_back(s3);
  v.push_back(s4);
  v.push_back(s5);

  int m = v[0].size();

  cout<<MaxLength(v, 0, m) + 1<<endl;

  return 0;
}

Java

// Java program to find longest
// String which is prefix String
// of at least two Strings
import java.util.*;
class GFG{
static int max1 = 0;

// Function to find Max length
// of the prefix
static int MaxLength(Vector<String> v,
                     int i, int m)
{
    // Base case
    if(i>=m)
    {
        return m-1;
    }

    // Iterating over all the alphabets
    for(int k = 0; k < 26; k++)
    {
        char c = (char)('a' + k);
        Vector<String> v1 = new Vector<String>();

        // Checking if char exists in
        // current String or not
        for(int j = 0; j < v.size(); j++)
        {
            if(v.get(j).charAt(i) == c)
            {
                v1.add(v.get(j));
            }
        }

        // If atleast 2 String have
        // that character
        if(v1.size() >= 2)
        {
           // Recursive call to i+1
           max1=Math.max(max1,
                         MaxLength(v1, i + 1, m));
        }
        else
        {
            max1=Math.max(max1, i - 1);
        }
    }
    return max1;
}

// Driver code
public static void main(String[] args)
{
  // Initialising Strings
  String s1, s2, s3, s4, s5;
  s1 = "abcde";
  s2 = "abcsd";
  s3 = "bcsdf";
  s4 = "abcda";
  s5 = "abced";

  Vector<String> v = new Vector<String>();

  // push Strings into vectors.
  v.add(s1);
  v.add(s2);
  v.add(s3);
  v.add(s4);
  v.add(s5);

  int m = v.get(0).length();
  System.out.print(MaxLength(v, 0, m) + 1);
}
}

// This code is contributed by shikhasingrajput

Python3

# Python3 program to find longest
# string which is prefix string
# of at least two strings

max1 = 0

# Function to find max length
# of the prefix
def MaxLength(v, i, m):

    global max1

    # Base case
    if(i >= m):
        return m - 1

    # Iterating over all the alphabets
    for k in range(26):
        c = chr(ord('a') + k)
        v1 = []

        # Checking if char exists in
        # current string or not
        for j in range(len(v)):
            if(v[j][i] == c):
                v1.append(v[j])

        # If atleast 2 string have
        # that character
        if(len(v1) >= 2):

            # Recursive call to i+1
            max1 = max(max1, MaxLength(v1, i + 1, m))
        else:
            max1 = max(max1, i - 1)

    return max1

# Driver code
if __name__ == '__main__':

    # Initialising strings
    s1 = "abcde"
    s2 = "abcsd"
    s3 = "bcsdf"
    s4 = "abcda"
    s5 = "abced"
    v = []

    # Push strings into vectors.
    v.append(s1)
    v.append(s2)
    v.append(s3)
    v.append(s4)
    v.append(s5)

    m = len(v[0])

    print(MaxLength(v, 0, m) + 1)

# This code is contributed by BhupendraSingh

C#

// C# program to find longest
// String which is prefix String
// of at least two Strings
using System;
using System.Collections.Generic;

class GFG{

static int max1 = 0;

// Function to find Max length
// of the prefix
static int MaxLength(List<String> v,
                     int i, int m)
{

    // Base case
    if (i >= m)
    {
        return m - 1;
    }

    // Iterating over all the alphabets
    for(int k = 0; k < 26; k++)
    {
        char c = (char)('a' + k);
        List<String> v1 = new List<String>();

        // Checking if char exists in
        // current String or not
        for(int j = 0; j < v.Count; j++)
        {
            if (v[j][i] == c)
            {
                v1.Add(v[j]);
            }
        }

        // If atleast 2 String have
        // that character
        if (v1.Count >= 2)
        {

            // Recursive call to i+1
            max1 = Math.Max(max1,
                            MaxLength(v1, i + 1, m));
        }
        else
        {
            max1 = Math.Max(max1, i - 1);
        }
    }
    return max1;
}

// Driver code
public static void Main(String[] args)
{

    // Initialising Strings
    String s1, s2, s3, s4, s5;
    s1 = "abcde";
    s2 = "abcsd";
    s3 = "bcsdf";
    s4 = "abcda";
    s5 = "abced";

    List<String> v = new List<String>();

    // push Strings into vectors.
    v.Add(s1);
    v.Add(s2);
    v.Add(s3);
    v.Add(s4);
    v.Add(s5);

    int m = v[0].Length;

    Console.Write(MaxLength(v, 0, m) + 1);
}
}

// This code is contributed by Amit Katiyar

Javascript

<script>
// Javascript program to find longest
// string which is prefix string
// of at least two strings

let max1=0;

// Function to find Max length
// of the prefix
function MaxLength(v, i, m)
{
    // Base case
    if(i>=m)
    {
        return m-1;
    }

    // Iterating over all the alphabets
    for(let k = 0; k < 26; k++)
    {
        let c = String.fromCharCode('a'.charCodeAt(0) + k);
        let v1 = [];

        // Checking if char exists in
        // current string or not
        for(let j = 0; j < v.length; j++)
        {
            if(v[j][i] == c)
            {
                v1.push(v[j]);
            }
        }

        // If atleast 2 string have
        // that character
        if(v1.length >= 2)
        {
            // Recursive call to i+1
            max1 = Math.max(max1, MaxLength(v1, i+1, m));
        }
        else
        {
            max1 = Math.max(max1, i - 1);
        }
    }
    return max1;
}

// Driver code

// Initialising strings
let s1, s2, s3, s4, s5;

s1 = "abcde";
s2 = "abcsd";
s3 = "bcsdf";
s4 = "abcda";
s5 = "abced";

let v = [];

// push strings into vectors.
v.push(s1);
v.push(s2);
v.push(s3);
v.push(s4);
v.push(s5);

let m = v[0].length;

document.write(MaxLength(v, 0, m) + 1 + "<br>");
</script>

Output:

4

Time Complexity: O(N*26)
Auxiliary Space: O(1)