String Checker IISit-in lab 4

Given a number of strings containing only “a”, “b”, “c”, “d”

Check each string that it follows the pattern anbmcmdn where m, n >= 1

Use only stack OR queue

Problem Description

Look at pattern: anbmcmdn

Notice that it is LIFO So we use a Stack!

Many ways of solving with a stack… here we show one way

Solution

Process one character from the input String at a time.

For example: for(int j = 0; j < s.length(); j++){

strCheck.nextChar(s.charAt(j));}

Solution

If character is “a”◦ We push to stack if

the stack is empty, or the top of the stack is “a”

◦ Else is not valid string

If character is “b”◦ Remember that we have a “b” (set a boolean flag)◦ We push to stack if

the stack is NOT empty, and the top of the stack is “a” or “b”

◦ Else is not valid string

Solution

We need to check this so that things like “bc” will be caught

If character is “c”◦ We pop from the stack if

the stack is NOT empty, and the top of the stack is “b”

◦ Else is not valid string

If character is “d”◦ We pop from the stack if

the stack is NOT empty, and the top of the stack is “a”, and there was a “b” read in (special check for things like “ad”)

◦ Else is not valid string

Solution

Finally, before concluding is valid string, check that stack is empty◦ We need this to catch things like “aaaaaabbccd”

(there will be many “a” left behind in the stack)

Solution

End

String Checker I