Concepts6
Think Backwards (Reverse Thinking)
Think Backwards is a problem‑solving pattern where you reverse time or direction so hard deletions become easy insertions and the final state becomes the starting point.
Z-Function
The Z-function of a string S computes for each position i the length of the longest substring starting at i that matches the prefix of S.
Exchange Arguments in DP
An exchange argument proves that any optimal solution can be reordered to satisfy a simple sorting rule by showing that swapping adjacent out-of-order elements never helps.
Digit DP
Digit DP is a dynamic programming technique for counting or aggregating values over all integers in a range that satisfy a digit-based property.
Lowest Common Ancestor (LCA)
The Lowest Common Ancestor (LCA) of two nodes in a rooted tree is the deepest node that is an ancestor of both.
Minimum Spanning Tree - Prim
Prim's algorithm builds a Minimum Spanning Tree (MST) by growing a tree from an arbitrary start vertex, always adding the lightest edge that connects the tree to a new vertex.