Good morning! Here's our prompt for today.

How would you write a function to detect a substring in a string?

If the substring can be found in the string, return the index at which it starts. Otherwise, return -1.

1function detectSubstring(str, subStr) {
2  return -1;
3}

Important-- do not use the native String class's built-in substring or substr method. This exercise is to understand the underlying implementation of that method.

Constraints

• Length of both the given strings <=100000
• The strings would never be null
• The strings will only consist of lowercase letters
• Expected time complexity : O(n)
• Expected space complexity : O(1)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

console.log('Running and logging statements.');

​

function detectSubstring(str, subStr) {

  // Fill in this method

  return str;

}

​

console.log(detectSubstring('ggraph', 'graph'));

console.log(detectSubstring('geography', 'graph'));

console.log(detectSubstring('digginn', 'inn'));

​

try {

  assert.equal(detectSubstring('thepigflewwow', 'flew'), 6);

​

  console.log(

    'PASSED: ' + "`detectSubstring('thepigflewwow', 'flew')` should return `6`"

  );

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(detectSubstring('twocanplay', 'two'), 0);

​

  console.log(

    'PASSED: ' + "`detectSubstring('twocanplay', 'two')` should return `0`"

  );

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