Remove all adjacent or consecutive duplicate characters

Remove all adjacent or consecutive duplicate characters

Input:  azxxzy
Output: ay
First "azxxzy" is reduced to "azzy". The string "azzy" contains duplicates, 
so it is further reduced to "ay".

Input: geeksforgeeg
Output: gksfor
First "geeksforgeeg" is reduced to "gksforgg". The string "gksforgg" contains 
duplicates, so it is further reduced to "gksfor".

Input: caaabbbaacdddd
Output: Empty String

Input: acaaabbbacdddd
Output: acac

Iterate through the characters and keep track of duplicates with start and end index, once you get a non matching character then delete the start to end characters and step back one more step and start again.

private static String removeAllAdjacentDuplicates(String s) {

StringBuilder sb = new StringBuilder(s);

int startIndex = -1;

int endIndex = -1;

char previousChar = '\0';

for (int i = 0; i < sb.length(); i++) {

if (previousChar == sb.charAt(i))

endIndex = i;

else {

if (endIndex > startIndex) {

sb.delete(startIndex, endIndex + 1);

i = --startIndex;

i = i < 0 ? 0 : i;

endIndex = -1;

}

startIndex = i;

previousChar = sb.charAt(i);

}

}

if (endIndex > startIndex)

sb.delete(startIndex, endIndex + 1);

return sb.toString();

}

Note: Deleting is a costly operation for that all the elements will be left shifted with their position.