hashTable.js

/*-----------------------------------------------------------------------------
the reference is from UdemyCourse: LearningDataStructuresinJavascriptFromScratch
-----------------------------------------------------------------------------*/

function HashTable(size) {
  this.buckets = Array(size);
  this.numBuckets = this.buckets.length;
}

function HashNode(key, value, next) {
  this.key = key;
  this.value = value;
  this.next = next || null;
  // 沒有next則給予null
}

HashTable.prototype.hash = function(key) {
  var total = 0;
  for (var i = 0; i < key.length; i++) {
    total += key.charCodeAt(i);
  }
  var buckets = total % this.numBuckets;
  return buckets;
  // buckets [0, 29]
};

HashTable.prototype.insert = function(key, value) {
  var index = this.hash(key);
  // if初始化；else找到尾巴加進去
  if (!this.buckets[index]) {
    this.buckets[index] = new HashNode(key, value);
  } else if (this.buckets[index].key === key) {
    this.buckets[index].value = value;
  } else {
    var currentNode = this.buckets[index];

    while (currentNode.next) {
      if (currentNode.next.key === key) {
        currentNode.next.value = value;
        return;
        // to stop the rest of this method from running
      }
      currentNode = currentNode.next;
    }
    currentNode.next = new HashNode(key, value);
  }
};

HashTable.prototype.get = function(key) {
  var index = this.hash(key);
  if (!this.buckets[index]) {
    return null;
  } else {
    var currentNode = this.buckets[index];
    while (currentNode) {
      if (currentNode.key === key) {
        return currentNode['value'];
      }
      currentNode = currentNode.next;
    }
    return null;
  }
};

// HashTable.prototype.getNode = function() {
//   for (var i in this.buckets) {
//     if (this.buckets[i] !== '') {
//       console.log(this.buckets[i]);
//     }
//   }
// };

HashTable.prototype.retrieveAll = function() {
  var allNode = [];
  for (var i = 0; i < this.numBuckets; i++) {
    var currentNode = this.buckets[i];
    while (currentNode) {
      allNode.push(currentNode);
      currentNode = currentNode.next;
    }
  }
  return allNode;
};

var myHT = new HashTable(30);
myHT.insert('Dean', '[email protected]');
myHT.insert('Megan', '[email protected]');
myHT.insert('Dane', '[email protected]');
myHT.insert('Dane', '[email protected]');
myHT.get('Dean');
// '[email protected]'

// return currentNode[value] 會變成 not defined
// 要寫成currentNode["value"];
// var obj = {a:['da',{dsa:12,jroe:13}], b:{}}
// obj[a]; 不行
// var a = "a"
// obj[a]; 可以


// 差別是我的子目錄指涵蓋最上頭的那一項目，而Dane在裡面。
// 官方解答除了包含我的邏輯外，還另外log出了下一層的項目。