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// description:  key is a have dictionary is b
const arr =[{ A: 'B'},{B:'C'},{C:'D'},{D:'E'},{E:'F'}]
//with addition case {F:'a'} => Infinity loop ,
//if db have this case will case error
/*expect:
A -F 
B-F
C-F
D-F
E-F

*/
//turn into 1 object have key is key and value
//
const keyValue = arr.reduce(function(result, item) {
  var key = Object.keys(item)[0]; 
  result[key] = item[key];
  return result;
}, {});

//array key to loop 
const mainKey = arr.flatMap(Object.keys)


const result ={}
let count =0;
for (let i=0; i< mainKey.length;i++) {
  count +=1
  let middleDictionary =[]
  let key = mainKey[i]
  let dictionary = keyValue[key]
  
  //exist loop before => have final key- value in dictionary
  //exp: case f:b => b have final => get from b
  //reduce some redundant loop
  if(result[dictionary]) {result[key] = result[dictionary];continue;}
  
  //if not above case => loop key first time
  if (!result[key]) result[key] =dictionary;
  while(keyValue[dictionary])
  {
    dictionary = keyValue[dictionary]
    count+=1
    middleDictionary.push(dictionary)
  }
  
  //save key that also distionary had been gone through
  //then update when final dictionary
  if(middleDictionary.length) 
  {
    for(let j=0; j< middleDictionary.length; j++) {
      
      //for case final dictionary - final dictionary
      if(keyValue[middleDictionary[j]]) 
      result[middleDictionary[j]] = dictionary
    }
  }
  result[key] =dictionary
}

const arrRes = Object.keys(result).map(i=> ({key :i, dictionary : result[i]}))

console.log('input key-dictionary is ', arr)
console.log('array key is',mainKey)
console.log('object have only key-value is', keyValue)
console.log('result is',result)
console.log('count is ', count)
console.log('final arr result', arrRes)