You must be stating the missionaries and cannibals problem incompletely. If only one person can fit on the boat at a time (which is essentially the case because you didn't say the person operating the boat is a missionary or cannibal, and you are implying that they must be operating the boat), it's provably impossible to solve. Wikipedia says you may have 1 or 2 people on the boat (as opposed to 0 or 1), which makes it relatively easy to solve as soon as you realize you can take people back that have already crossed.
The correct solution requires that you get out of the boat and put two cannibals on it. The statement that the boat holds "only you" and one other person very strongly implies that is not allowed.
