greedychoice

Greedychoice is a design principle in algorithm design characterized by constructing a solution through a sequence of locally optimal choices, with the aim that these choices lead to a globally optimal solution.

A problem is considered amenable to greedy methods if it has the greedy-choice property: there exists an optimal solution that contains the locally optimal choice made at the current step. Many greedy algorithms also rely on the problem having an optimal substructure, so that solving subproblems contributes to a global optimum. Correctness is often established with an exchange argument, showing that any optimal solution can be transformed to include the current greedy choice without losing optimality.

In practice, greedy algorithms proceed by repeatedly selecting the best available option according to a fixed criterion and discarding choices that would create conflicts or infeasibilities in the remainder of the process. This yields simple and efficient procedures, often with time complexities that are competitive with more general methods.

Common examples include the activity selection problem, which can be solved by choosing activities with the earliest finish times; Kruskal’s and Prim’s algorithms for minimum spanning trees, which add the lightest edges that connect previously disconnected components; Dijkstra’s algorithm for shortest paths in graphs with non-negative weights, which always extends the nearest unvisited vertex; and Huffman coding, which constructs optimal prefix codes by repeatedly merging the two least probable symbols.

Limitations exist: not all problems admit a greedy solution, and some require dynamic programming or backtracking. Greedy choice may fail to yield an optimal result for such cases, underscoring the need to verify the greedy-choice property for each problem.