Red-Black Trees: A Type of Balanced Binary Tree, Understanding Its Rules Simply

A red-black tree is a self-balancing binary search tree that ensures balance through color marking and five rules, resulting in stable insertion, deletion, and search complexities of O(log n). The core rules are: nodes are either red or black; the root is black; empty leaves (NIL) are black; red nodes must have black children (to avoid consecutive red nodes); and the number of black nodes on any path from a node to its descendant NIL leaves (black height) is consistent. Rule 4 prevents consecutive red nodes, while Rule 5 ensures equal black heights, together limiting the tree height to O(log n). Newly inserted nodes are red, and adjustments (color changes or rotations) are performed if the parent is red. Widely used in Java TreeMap and Redis sorted sets, it enables efficient ordered operations through its balanced structure.