backspace-string-compare.py

# Time:  O(m + n)
# Space: O(1)

# Given two strings S and T, return if they are equal
# when both are typed into empty text editors. # means a backspace character.
#
# Example 1:
#
# Input: S = "ab#c", T = "ad#c"
# Output: true
# Explanation: Both S and T become "ac".
# Example 2:
#
# Input: S = "ab##", T = "c#d#"
# Output: true
# Explanation: Both S and T become "".
# Example 3:
#
# Input: S = "a##c", T = "#a#c"
# Output: true
# Explanation: Both S and T become "c".
# Example 4:
#
# Input: S = "a#c", T = "b"
# Output: false
# Explanation: S becomes "c" while T becomes "b".
#
# Note:
# - 1 <= S.length <= 200
# - 1 <= T.length <= 200
# - S and T only contain lowercase letters and '#' characters.

import itertools

try:
    xrange          # Python 2
except NameError:
    xrange = range  # Python 3


class Solution(object):
    def backspaceCompare(self, S, T):
        """
        :type S: str
        :type T: str
        :rtype: bool
        """
        def findNextChar(S):
            skip = 0
            for i in reversed(xrange(len(S))):
                if S[i] == '#':
                    skip += 1
                elif skip:
                    skip -= 1
                else:
                    yield S[i]

        return all(x == y for x, y in
                   itertools.izip_longest(findNextChar(S), findNextChar(T)))