[JS] Matching pairs

matchingPairs.js

function getCharactersDistribution(string) {
  const result = {};
  string.split("").forEach((char, idx) => {
    if(result[char])  result[char].add(String(idx));
    else result[char] = new Set([String(idx)]);
  });
  return result;
}

function matchingPairs(s, t) {
  const primaryTargets = {};
  let secondaryTargetsCount = 0;
  const tMap = getCharactersDistribution(t);
  let matchingPairs = 0;
  s.split('').forEach((char, idx) => {
    if(tMap[char]) {
      if(tMap[char].has(String(idx))) {
        matchingPairs++;
      }
      else {
        primaryTargets[idx] = tMap[char]; 
      }
    }
    else {
      secondaryTargetsCount++;
    }
  });

  if(Object.keys(primaryTargets).length > 0) {
    for(let idx of Object.keys(primaryTargets)) {
      const desiredIndexes = primaryTargets[idx];
      for(let idx2 of desiredIndexes) {
        if(primaryTargets[idx2].has(idx)) return matchingPairs + 2;
      }
    }
    return matchingPairs + 1;
  }
  if(secondaryTargetsCount > 1) {
    return matchingPairs;
  }
  if(secondaryTargetsCount === 1) {
    return Math.max(matchingPairs - 1, 0);  
  }
  return Math.max(matchingPairs - 2, 0);  
}


// ---------------------------------------------------------- Test ---------------------------------------- //
console.log(matchingPairs('', '')); // 0 [could be change to throw an error since it wasnt possible to swap]
console.log(matchingPairs('a', 'a')); // 0 [could be change to throw an error since it wasnt possible to swap]
console.log(matchingPairs('a', 'b')); // 0 [could be change to throw an error since it wasnt possible to swap]
console.log(matchingPairs('ab', 'ab')); // 0
console.log(matchingPairs('ab', 'ba')); // 2
console.log(matchingPairs('abcd', 'dcba')); // 2
console.log(matchingPairs('abcde', 'adcbe')); // 5
console.log(matchingPairs('abc', 'abe')); // 1
console.log(matchingPairs('abcd', 'abef')); // 2