Short Problem Definition:
Steve has a string of lowercase characters in range ascii[‘a’..’z’]. He wants to reduce the string to its shortest length by doing a series of operations. In each operation he selects a pair of adjacent lowercase letters that match, and he deletes them. For instance, the string aab could be shortened to b in one operation.
Steve’s task is to delete as many characters as possible using this method and print the resulting string. If the final string is empty, print Empty String
Link
Complexity:
time complexity is O(N)
space complexity is O(N)
Execution:
The solution creates a stack of values. If the top value on the stack is equivalent to the next value, simply remove both. This solution assumes that there are only ever 2 values next to each other. If any adjacent values were to be removed, I would require more loops.
Solution:
i = raw_input()
s = []
for c in i:
if not s:
s.append(c)
else:
if s[-1] == c:
s.pop()
else:
s.append(c)
if not s:
print "Empty String"
else:
print ''.join(s)