For the following problems, you are driving through a portion of a city, and must go from the start to the finish by passing through the required number of intersections (no more, no less). All roads are two-way, but u-turns are illegal, and you must stay within the outlined area. Additionally, you must follow an if-then-else statement which relates possible actions at each intersection (either turning left, turning right, or going straight). In the actual puzzles, each city section has multiple if-then-else statements, and each statement produces a different path through the city.

Here's an example to help you get the idea:

Pass through THREE intersections.

If you go straight at the first intersection,

then go straight at the third intersection,

otherwise turn left at the second intersection. Given the layout and the boundaries of this portion of the city, there are only two possible ways to go from the start to the finish in just three intersections. Both are shown below. Now we need to figure out which possibility is eliminated with the clue.Assuming we go straight at the first intersection, we then are supposed to go straight at the third intersection. Unfortunately, this forces us to leave the designated area at the wrong location. We can't circle around and try again, since we’re only supposed to pass through three intersections. Instead, what if we don't go straight at the first intersection? Then we are supposed to turn left at the second intersection. We can still go straight at the third intersection to complete the puzzle, since this does not violate the if-then-else statement. When the "if" part is false, the "then" part could be true or false, but the "else" part must be true.

Here's another slightly more complicated example:

Pass through FIVE intersections.

If you go right at the second intersection,

then go left at the fourth intersection,

otherwise go straight at the fifth intersection.Again, given the layout and the boundaries of this portion of the city, there are only three possible ways to go from the start to the finish in just five intersections. Each possibility is shown below, and now we need to figure out which two are eliminated with the clue.

Notice that this clue tells us nothing about what to do at the first or third intersections, so we can do as we please there.

We have two choices at the first intersection. If we turn right, then we'll have to turn left at the second intersection in order to pass through five intersections. Since we turn left at the second intersection, we have to go straight at the fifth intersection. Unfortunately, to end at the finish we'd need to turn left. If we go straight at the first intersection, we have to turn right at the second intersection. We now have two options for the third intersection. If we go straight, it would be nice to turn right at the fourth intersection. But according to the clue, we must turn left, which leads us out of the designated area too soon. Going straight at the first intersection, then right at the third intersection allows us to turn left at the fourth intersection and go straight at the fifth, exiting the city blocks in the proper spot.

Last updated: April 30, 2004

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