dfs-preorder.js

dfs-preorder.js

  preOrder(result=[]) {
    if (!this.left && !this.right) {
      return result.push(this.key);
    }
    result.push(this.key);
    if (this.left) {
      this.left.preOrder(result);
    }
    if (this.right) {
      this.right.preOrder(result);
    }
    return result;
  }