The next mayor of Minneapolis will be elected by a relatively new process called ranked-choice voting. Here's how it works:
If no candidate wins a majority of votes in the first round, all votes must be tallied before a winner can be declared.
To correctly determine how to redistribute votes from eliminated candidates, one must know the order of rankings on each ballot. With a small field of candidates, this is not very difficult. But the possible combinations of ballot rankings increases exponentially with more candidates.
In the 2013 Minneapolis mayoral election, there will be 35 candidates on the ballot. Without considering a single write-in, this means there are 39,270 possible rankings.
The city of Minneapolis will use an electronic system to determine the winner, so such calculations will take little time. But by law, recounts must be performed by hand, so this complexity may still be a factor.
If such tallying is required (by computer or by hand), the city of Minneapolis won't announce the winners of ranked-choice races until the day after the election — at the earliest.