常见数据结构之二叉搜索树

二叉搜索树(Binary Search Tree)指左子树的值小于根节点的值，右子树的值大于根节点的值。

BTS 基本结构:

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

function Tree() {
  this.root = null;
}

Tree.prototype = {
  insert,
  getMin,
  getMax,
  getDeep,
};

BTS 插入数据：

function insert(val) {
  this.root = insertNode(this.root, val);
  function insertNode(root, val) {
    if (!root) {
      return new Node(val);
    }
    if (val < root.val) {
      root.left = insertNode(root.left, val);
    } else if (val > root.val) {
      root.right = insertNode(root.right, val);
    }
    return root;
  }
}

查找最大最小值：

function getMax() {
  let current = this.root;
  while (current) {
    if (!current.right) {
      return current;
    }
    current = current.right;
  }
}

function getMin() {
  let current = this.root;
  while (current) {
    if (!current.left) {
      return current;
    }
    current = current.left;
  }
}

获取树的深度

function getDeep(node, deep) {
  deep = deep || 0;
  if (node === null) {
    return deep;
  }
  deep++;
  let dleft = this.getDeep(node.left, deep);
  let dright = this.getDeep(node.right, deep);
  return Math.max(dleft, dright);
}

前序遍历：

function preOrder(node) {
  const stack = [];
  while (node || stack.length) {
    while (node) {
      console.log(node.val);
      stack.push(node); // stack 储存父节点
      node = node.left; // 去找左儿子
    }
    node = stack.pop();
    node = node.right; // 去找右儿子
  }
}

中序遍历：

function inOrder(node) {
  let stack = [];
  while (stack.length || node) {
    while (node) {
      stack.push(node);
      node = node.left;
    }
    node = stack.pop();
    console.log(node.val);
    node = node.right;
  }
}

后序遍历:

function postOrder(node) {
  const stack = [];
  let cur = node;
  let last = null;
  while (cur || stack.length) {
    while (cur) {
      stack.push(cur);
      cur = cur.left;
    }
    cur = stack[stack.length - 1];
    if (!cur.right || cur.right === last) {
      cur = stack.pop();
      console.log(cur.val);
      last = cur;
      cur = null;
    } else {
      cur = cur.right;
    }
  }
}