Search through a string using sliding window algorithm.

sliding window algorithm search string.js

/* 
 Sliding window involves creating a window which can either be an array or number from one
 position to another.
 
 Depending on a certain condition, the window either increases or closes (and new window is created)
 Very uselful for keeping track of subset of data in an array/string etc.
*/


/**
 * @desc The function find substring in a string and return number of times the substring is found using sliding window algorithm
 * @param {String} longString Where to search a substring
 * @param {String} shortString The substring to be looked up
 * 
 * @returns {Number} number of found instances of shortString * 
 */
function search(longString, shortString) {
    let currentSubString = '';
    let counter = 0;
    if (shortString > longString.length) return null;
  
    for (let i = 0; i < shortString.length; i ++) {
      currentSubString += longString[i]; // Get the first n (length of substring) characters from a longString: Hel 
    }
    
    // check whether the first n (length of substring) characters of the longString is equal to shortString and increment the counter
    if (currentSubString === shortString) {
        counter++;
    }
  
    for (let i = shortString.length; i < longString.length + 1; i ++) {
      // Remove the first character and add the nth character:
      // first loop: Hel => ell
      currentSubString = currentSubString.substring(1) + longString[i] 

      // compare if the current substring is equal to short string:
      // first loop: ell == lol
      if (currentSubString === shortString) {
        counter ++;
      }
    }
  
    return counter;
  }
  
  search('Hello loled', 'lol')

// Native javascript search
function nativeSearch (long, short) {
    var count = 0;
    for (var i = 0; i < long.length; i++) {
        for (var j = 0; j < short.length; j++) {
            if (short[j] !== long[i+j]) break;
            if (j === short.length - 1) count++;
        }
    }

    return count;
}