【アルゴリズムの基礎】二分木 preorder, inorder, postorder, hierarchy, depth first (preorder), width first (hierarchy) traversal

二分木走査 [C++] https://blog.csdn.net/gatieme/article/details/51163010
二分木走査 [Java] https://www.cnblogs.com/llguanli/p/7363657.html
二分木走査 [ Python] https://my.oschina.net/magicalee/blog/2209301