Can we color the vertices of a planar graph with four colors such that no two adjacent vertices have the same color?

Given a weighted graph and two vertices, find the shortest path between them.

Given a weighted graph, find a subgraph that connects all vertices with the minimum total edge weight.

Pearls In Graph Theory Solution Manual

Can we color the vertices of a planar graph with four colors such that no two adjacent vertices have the same color?

Given a weighted graph and two vertices, find the shortest path between them.

Given a weighted graph, find a subgraph that connects all vertices with the minimum total edge weight.