class Solution {
  findWordConcatenation(str, words) {
    const resultIndices = [];
    const wordLen = words[0].length;
    const numWords = words.length;
    const totalLen = wordLen * numWords;
    // TODO: Write your code here
    let wordsFreqMap = new Map();
    for(let i=0; i<words.length; i++) {
      wordsFreqMap.set(words[i], (wordsFreqMap.get(words[i]) || 0) + 1);
    }
    const uniqueWordsToMatch = wordsFreqMap.size;
    for (let offset = 0; offset < wordLen; offset++) {
      let windowStart = offset;
      let windowEnd = offset;
      let wordsMatched = 0;
    const currWordsCount = new Map();

      while(windowEnd + wordLen <= str.length) {
        const currWord = str.substring(windowEnd, windowEnd + wordLen);
        windowEnd += wordLen;
        if(wordsFreqMap.has(currWord)) {
          currWordsCount.set(currWord, (currWordsCount.get(currWord) || 0) + 1);
          if(currWordsCount.get(currWord) === wordsFreqMap.get(currWord)) {
            wordsMatched++;
          }else if(currWordsCount.get(currWord) === wordsFreqMap.get(currWord) + 1) {
            wordsMatched--;
          }
        }

        if(windowEnd - windowStart > totalLen) {
          const startWord = str.substring(windowStart, windowStart + wordLen);
          windowStart += wordLen;

          if(wordsFreqMap.has(startWord)) {
            if(currWordsCount.get(startWord) === wordsFreqMap.get(startWord)) {
              wordsMatched--;
            }else if(currWordsCount.get(startWord) === wordsFreqMap.get(startWord) + 1) {
              wordsMatched++;
            }
            currWordsCount.set(startWord, currWordsCount.get(startWord) - 1);
          }
        }

        if(wordsMatched === uniqueWordsToMatch) {
          resultIndices.push(windowStart);
        }
      }
    }
    return resultIndices;
  }
}