Good evening! Here's our prompt for today.

Given two strings, one named sub and the other str, determine if sub is a subsequence of str.

1const str = "barbell"
2const sub = "bell"
3isASubsequence(sub, str);
4// true

For the sake of the exercise, let's assume that these strings only have lower case characters.

What is subsequence? You can think of it as a substring, but the letters don't have to be adjacent. It is formed from the base string by deleting some or none of the characters without affecting the relative positions of the other letters. So this also works:

1const str = "chicken"
2const sub = "hen"
3isASubsequence(sub, str);
4// true

Constraints

• Length of both the strings <= 100000
• The strings will contain only alphanumeric characters (a-z , A-Z, 0-9)
• The strings can be empty
• 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');

​

/**

 *  @param {string} sub

 *  @param {string} str

 *  @return {boolean}

 */

function isASubsequence(sub, str) {

  // fill this in

  return true;

}

​

try {

  assert.deepEqual(isASubsequence('c', 'co'), true);

​

  console.log('PASSED: ' + "isASubsequence('c','co') should return true");

} catch (err) {

  console.log(err);

}

​

try {

  assert.deepEqual(isASubsequence('liblu', 'egi'), false);

​

  console.log('PASSED: ' + "isASubsequence('liblu','egi') should return false");

} catch (err) {

  console.log(err);

}

​

try {

Here's how we would solve this problem...

How do I use this guide?