Concept: Binary Search Tree

Tree is born for search as its name.

This is a binary tree, that is, a root node has only two Subtrees. Left subtree <root node <right subtree. Of course, left and right subtree can be empty. The smaller value indicates all nodes, that is, the root node is greater than all nodes in the left subtree. If one of the nodes in the left subtree is greater than the root node, you cannot. (Otherwise, you won't be able to find it)

Then recursion goes down. The left subtree, as the root node, also meets this requirement and is itself a binary search tree.

Purpose: quick search.

Greater than the root, go to the right, less than the root, go to the left until the target is found, and if the target exists, it is absolutely impossible to miss the target.