So it would appear that indeed tougher challenges are given at weekends and that they are more likely to contain the type of puzzle requiring optimised reengineering to solve the second part. It is perhaps just as well that during the week, challenge difficulty eases off towards Friday in preparation for a tough weekend.

Updates

The article above was written on Day 17 (Saturday) of the 2016 challenge. Here are some updates as new challenges are released.

The Saturday night / Sunday morning Day 18 challenge was easier than had been typical for a weekend in week three so the weekday-weekend difficulty levels have balanced a little.

Sunday night / Monday morning's present steeling problem was uncharacteristically challenging for a Monday particularly as many of the heuristics used for tackling the first part did not apply in the second. This required many to spend time thinking of alternative approaches.

The Monday night / Tuesday morning Day 20 challenge was relatively straightforward and more typical of a mid-week problem, although judging by completion times of the two parts, many on the leaderboard had to re-engineer their solutions somewhat for part two.

Tuesday/Wednesday's challenge was one that took a little time to set up, but was comparatively easy to solve (at least for the first part). This is perhaps an example of a challenge where the time taken by those on the leaderboard is not necessarily indicative of difficulty.

Wednesday/Thursday's grid cell swapping puzzle was one of the harder ones for those who didn't spot the 'trick' subtly hidden in the way the question was expressed. Perhaps those rushing for a leaderboard position are less likely to spot these tricks than if not under time pressure. The final week of the AoC seems to be showing a pattern of more difficult challenges. So far, the Friday questions have tended to be the easier ones. Will the last Friday buck the trend?

The Thursday/Friday assembunny revisited challenge keeps the trend of slightly more time consuming final week. What will the final Christmas weekend bring us?

The penultimate puzzle – robot maze traversal – challenged a few despite having much in common with previous graph traversal problems this year. It is notable that most of the effort was in constructing a reasonably efficient way of evaluating alternative traversals even to answer the first part. The second part become a trivial addition and is reflected in in the low part two completion time. Overall this brought Saturday up as the most challenging day on average and confirms a final week of tougher puzzles.

As last year, the final Christmas assembunny code challenge didn't tax too many people too much and allowed previous assembunny solutions to be built upon to earn a gold star. This rounded off a slightly more challenging but achievable final Advent of Code week.