Remember that an ASCII character is an
8 bit number, and its value ranges from 0 and 255. An array of 256 booleans provides an efficient buffer to keep a track of encountered characters.
1. If the input is null [Empty], return true.
2. Create an array of 256 booleans. boolean[] arr = new boolean[256]
3. If you write int pos = str.charAt(i), the ith character of the string str will be cast to a number between 0 and 255
4. Run a for loop across the input String. Check the [0..255]th index in the boolean array. The index is the number obtained in the previous step.
5. If that position is false, mark it true. If it is true, it implies that you have encountered the character before and hence there is a repetition. Return false
6. At the end of the for loop, return true.
