- 159 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 160 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 161 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 162 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 163 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 164 -

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo

- 165 -

Suppose that the optimum cover has k sets. Then at a stage where r items remain to be covered, some set covers r/k of them. Therefore, choosing the set that covers the most new points reduces the number of uncovered points to r − r/k = r(1 − 1/k). If we start with n points and repeat this process n times, r ≤ n(1 − 1/k)j . Since r is an integer, we are done when n(1 − 1/k)j < 1. This happens when j = O(k log n). Hence, α = j/k = O(log n).

CS 466 Fall 2019 Lecture 13 - Approximation Algorithms Anna LubiwUniv. Waterloo