In 1852, botanist Francis Guthrie noticed something peculiar as he was coloring a map of counties in England. Despite the counties’ meandering shapes and varied configurations, four colors were ...

"This is a new way to package a problem so that a quantum computer ... the PNNL team turned to a type of algorithm known as graph coloring—a specialty of Ferdous and Halappanavar.

for this kind of problem. The new algorithm also has to work through too many steps for most real-world applications, where the relevant graphs are usually simple enough to check with brute-force ...

Graph coloring problems tend to be simple to state, but they are often enormously hard to solve. Even the question that launched the field — Do four colors suffice to color any map? — took more than a ...