JavaScript: Find the longest common starting substring in a set of strings

JavaScript Array: Exercise-28 with Solution

Longest Common Starting Substring

Write a JavaScript function to find the longest common starting substring in a set of strings.

Sample array : console.log(longest_common_starting_substring(['go', 'google']));
Expected result : "go"

Visual Presentation:

Sample Solution:

JavaScript Code:

// Function to find the longest common starting substring in an array of strings
function longest_common_starting_substring(arr1) {
  // Create a sorted copy of the input array
  var arr = arr1.concat().sort(),
      // Get the first and last strings after sorting
      a1 = arr[0],
      a2 = arr[arr.length - 1],
      // Get the length of the first string
      L = a1.length,
      // Initialize an index variable
      i = 0;

  // Iterate through the characters of the first string until a mismatch is found
  while (i < L && a1.charAt(i) === a2.charAt(i)) {
    i++;
  }

  // Return the longest common starting substring using substring(0, i)
  return a1.substring(0, i);
}

// Output the result of the longest_common_starting_substring function with sample arrays
console.log(longest_common_starting_substring(['go', 'google'])); // Output: 'go'

console.log(longest_common_starting_substring(['SQLInjection', 'SQLTutorial'])); // Output: 'SQL'

console.log(longest_common_starting_substring(['abcd', '1234'])); 

Output:

go
SQL

Flowchart:

ES6 Version:

// Function to find the longest common starting substring in an array of strings
const longest_common_starting_substring = (arr1) => {
  // Create a sorted copy of the input array
  const arr = [...arr1].sort();
  // Get the first and last strings after sorting
  const a1 = arr[0];
  const a2 = arr[arr.length - 1];
  // Get the length of the first string
  const L = a1.length;
  // Initialize an index variable
  let i = 0;

  // Iterate through the characters of the first string until a mismatch is found
  while (i < L && a1.charAt(i) === a2.charAt(i)) {
    i++;
  }

  // Return the longest common starting substring using substring(0, i)
  return a1.substring(0, i);
};

// Output the result of the longest_common_starting_substring function with sample arrays
console.log(longest_common_starting_substring(['go', 'google'])); // Output: 'go'

console.log(longest_common_starting_substring(['SQLInjection', 'SQLTutorial'])); // Output: 'SQL'

console.log(longest_common_starting_substring(['abcd', '1234'])); 

Live Demo:

See the Pen JavaScript - Find the longest common starting substring in a set of strings - array-ex- 28 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that finds the longest common prefix among an array of strings using horizontal scanning.
• Write a JavaScript function that uses vertical scanning to determine the longest common starting substring.
• Write a JavaScript function that handles edge cases such as empty arrays and returns an empty string if no common prefix exists.
• Write a JavaScript function that iterates character by character to find the common starting substring of a set of strings.

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