The first step is to interpret the problem. At first glance you might think this problem is a difficult one, and that was my initial reaction as well. Realizing the setup of the question was the first step. Knowing you could not leave the cat and dog together, and you could not leave the cat and mouse together, the next step is to figure out what it is your strategy is going to be. What strategy did you use and how did you evaluate your progress? For my first attempt at my strategy my cat died many many times.
I started with taking the cat over, and then the mouse, but as soon as I went back for the dog, my mouse would die. If I took the cat, and then the dog, then the cat would die. Using “Hill climbing” aided me in my strategy to getting all three animals across the stream. Each step I moved closer to getting all three animals safely across the river. One step at a time and the death of many animals, I finally realized that I didn’t have to leave the animals on the other side of the river.
When I discovered that I could take back an animal it made the task that much easier. Did you encounter any obstacles while solving the problem? The biggest obstacle for me was getting over the assumption that I had to leave the animals on the other side of the river once I had taken them there. Another obstacle I had was trying to out think myself. Every time I couldn’t get the right answer I would try to make the test harder than it was. Trying to over think the problem really set up one of the biggest road blocks of the problem for me.
Were you aware of this thought process as you worked through the problem? I was not aware of the different processes I was using until after the problem was solved. Then I was able to look at my though process and see what I had used to get to the solution. I knew that I had to take the animals across the river in a certain order, but I didn’t know which order that was. I did try to take two animals at a time but that didn’t work either. If I could have taken the dog and the mouse at the same time I would have been done in a heartbeat.