My guess is you can start off with placing each character in a bit vector. Initially the counter will be zero. As you go on adding the characters to the bit vector, the value of counter associated to the particular index will increase each time the same random character is encountered. After all the characters have been put in the bit vector run the for loop for i 0 to 255 and put an if condition that will print the characters only if the value of the counter is greater than zero.