摘要：有關(guān)算法，數(shù)據(jù)結(jié)構(gòu)的代碼已上傳至算法與數(shù)據(jù)結(jié)構(gòu)。構(gòu)造函數(shù)深度優(yōu)先遍歷廣度優(yōu)先遍歷插入中序遍歷前序遍歷后序遍歷聲明一棵樹聲明一個(gè)節(jié)點(diǎn)相關(guān)算法深度優(yōu)先遍歷深度優(yōu)先遍歷，先查看左孩子是否存在，若存在，傳入遞歸，否則，再查看右孩子。

這次來(lái)了解一下二叉樹，以及相應(yīng)的算法。以下代碼并非所有都由本人所寫，只是在此分享出來(lái)，以便大家學(xué)習(xí)。

有關(guān)javascript算法，數(shù)據(jù)結(jié)構(gòu)的代碼已上傳至 javascript算法與數(shù)據(jù)結(jié)構(gòu)。

/**
 *        使用js實(shí)現(xiàn)一個(gè)二叉樹。
 *        Tree        構(gòu)造函數(shù)
 *        traverseDF  深度優(yōu)先遍歷
 *        traverseBF  廣度優(yōu)先遍歷
 *        insert      插入
 *        inOrderTraverse中序遍歷
 *        preOrderTraverse前序遍歷
 *        postOderTraverse后序遍歷
 */

聲明一棵樹：

function Tree () {
    this._root;
}

聲明一個(gè)節(jié)點(diǎn)：

function Node (data) {
    this.data = data;
    this.left = null;
    this.right = null;
}

/**
 *    深度優(yōu)先遍歷，先查看左孩子是否存在，若存在，傳入recurse遞歸，
 *    否則，再查看右孩子。若都不存在，對(duì)該節(jié)點(diǎn)執(zhí)行callback操作。
 */
Tree.prototype.traverseDF = function (callback) {
  (function recurse (currentNode) {
     if (currentNode.left) {
       recurse(currentNode.left);
     }
     if (currentNode.right) {
       recurse(currentNode.right);
     }
     callback(currentNode);
  })(this._root)
}

/**
 *    寬度優(yōu)先遍歷借助隊(duì)列來(lái)實(shí)現(xiàn)。
 */
Tree.prototype.traverseBF = function (callback) {
  var queue = new Queue();
  if (!this._root) {
    console.log("empty tree");
    return;
  }
  queue.enqueue(this._root);
  var currentNode = queue.dequeue();
  while (currentNode) {
    if (currentNode.left) {
      queue.enqueue(currentNode.left);
    }
    if (currentNode.right) {
      queue.enqueue(currentNode.right);
    }
    callback(currentNode);
    currentNode = queue.dequeue();
  }
}

/**
 *     插入節(jié)點(diǎn)用到了寬度優(yōu)先遍歷的思想
 */

Tree.prototype.insert = function (data) {
    var node = new Node(data);
    var message = {
        success: "Inserted successfully!",
    }
    if (!this._root) {
        this._root = node;
        return;
    }
    var queue = new Queue();
    queue.enqueue(this._root);
    var currentNode = queue.dequeue();
    while (currentNode) {
        if (currentNode.left) {
            queue.enqueue(currentNode.left);
        } else {
            currentNode.left = node;
            console.log(message.success);
            return;
        }
        if (currentNode.right) {
            queue.enqueue(currentNode.right);
        } else {
            currentNode.right = node;
            console.log(message.success);
            return;
        } 
        currentNode = queue.dequeue();
    }
}

/**
 *     中序遍歷
 */
Tree.prototype.forInOrder = function (node) {
    if (node) {
        this.forInOrder(node.left);
        console.log(node.data);
        this.forInOrder(node.right);
    }
}

Tree.prototype.inOrderTraverse = function () {
    this.forInOrder(this._root);
}

中序遍歷的非遞歸算法

/**
 *   借助一個(gè)棧，先沿著左子樹到葉節(jié)點(diǎn)，依次入棧，
 * 再出棧遍歷，對(duì)該棧頂節(jié)點(diǎn)的右子樹進(jìn)行統(tǒng)一的操作
 */

Tree.prototype.inOrder = function (callback) {
  var currentNode = null;
  if (this.root) {
    currentNode = root;
  } else {
    return;
  }
  var stack = [];
  do {
    while (currentNode != null) {
      stack.push(currentNode);
      currentNode = currentNode.left;
    }
    if (!stack.length) {
      stack.pop(currentNode);
      callback(currentNode);
      currentNode = currentNode.right;
    }
  } while (currentNode !== null && stack.length)
}

/**
 *    前序遍歷
 */
Tree.prototype.forPreOrder = function (node) {
    if (node) {
        console.log(node.data);
        this.forPreOrder(node.left);
        this.forPreOrder(node.right);
    }
}

Tree.prototype.preOrderTraverse = function () {
    this.forPreOrder(this._root);
}

當(dāng)然還有前序遍歷的非遞歸算法。

/**
 *  算法關(guān)鍵思想是用棧為右子樹預(yù)留位置。
 *  可以利用數(shù)組作為一個(gè)棧。
 */
Tree.prototype.preOrder = function (callback) {
  var currentNode = null;
  if (this.root) {
    currentNode = this.root;
  } else {
    return;
  }
  var stack = [];
  while (currentNode) {
    callback(currentNode);
    if (currentNode.right) {
      stack.push(currentNode.right);
    }
    if (currentNode.left) {
      currentNode = currentNode.left;
    } else {
      currentNode = stack.pop();
    }
  }
}

/**
 *    后序遍歷
 */
Tree.prototype.forPostOrder = function (node) {
    if (node) {
        this.forPostOrder(node.left);
        this.forPostOrder(node.right);
        console.log(node.data);
    }
}

Tree.prototype.postOderTraverse = function () {
    this.forPostOrder(this._root);
}

function Queue () {
    this._oldestIndex = 1;
    this._newestIndex = 1;
    this._storage = {};
}

Queue.prototype.enqueue = function (data) {
    this._storage[this._newestIndex] = data;
    this._newestIndex++;
}

Queue.prototype.dequeue = function () {
    var oldestIndex = this._oldestIndex,
        newestIndex = this._newestIndex,
        deletedData;
    if (oldestIndex !== newestIndex) {
        deletedData = this._storage[oldestIndex];
        delete this._storage[oldestIndex];
        this._oldestIndex++;
        return deletedData;
    }
    return null;
}