You are given a box of matches and a piece of ropes. For example, if you light the rope at one end, it will take exactly 60 minutes before the entire rope has burnt up, How can you measure a period of exactly 30 minutes? You can choose the starting time. More precisely, given the matches and the rope, you are to say the words “start” and “done” exactly 30 minutes apart.? There are three boxes, one contains only apples, one contains only oranges, and one contains both apples and oranges. The boxes have been incorrectly labeled such that no label identifies the actual contents of the box it labels. Opening just one box, and without looking in the box, you take out one piece of fruit. By looking at the fruit, how can you immediately label all of the boxes correctly? Count of duplicate chars even or odd without divide symbol
