Actually, no windows shrinking is required to solve the task. We jus go forward and keep track if we found a pattern or not. Just rephrase the task like this: Find out if there is a substring in a string that contains the same characters as in the pattern regardless the order. The task now becomes much simpler :) Solution in JS:

const f = (_str, _pattern) => { let patternLength = _pattern.length; let numberOfMatches = 0;

//transform to an array to use the splice method let _patternArr = [..._pattern];

// Algorithm idea: all the char in the pattern regardless the order // should be found in a substring.

//Just reset the pattern if a foreign char is found for (let windowEnd = 0; windowEnd < _str.length; windowEnd++) { const rightChar = _str[windowEnd]; const index = _patternArr.indexOf(rightChar);

// if we found a match, remove it from the pattern if (index >= 0) { numberOfMatches += 1; _patternArr.splice(index, 1); } else { // if we found a foreign char, reset the pattern to initial state numberOfMatches = 0; _patternArr = [..._pattern]; } if (numberOfMatches === patternLength) return true; } return false; };