Vertex Cover 2-Approx Size

Problem

Return the size of the vertex cover produced by the maximal-matching 2-approximation.

Scan edges in order and, whenever both endpoints are still unmatched, add both endpoints to the cover and mark them used. The result is twice a maximal matching, hence at most twice the optimal cover; return 0 for non-positive n.

Hint

Any vertex cover must contain at least one endpoint of every matching edge.

Test cases

case 1

in: [3,[[0,1],[1,2],[2,0]]]

expected: 2

case 2

in: [4,[[0,1],[0,2],[0,3]]]

expected: 2

case 3

in: [4,[[0,1],[1,2],[2,3]]]

expected: 4

case 4

in: [3,[]]

expected: 0

case 5

in: [2,[[0,1]]]

expected: 2

Starter codePython

def vertex_cover_approx_size(n, edges):
    # Your code here
    pass

5 test cases · run your code against them in the editor