leetcode844 Backspace String Compare

 """
 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".
 """
 """
 简单题通过
 """
 class Solution:
     def backspaceCompare(self, S, T):
         """
         :type S: str
         :type T: str
         :rtype: bool
         """
         return self._back(S) == self._back(T)
     def _back(self, string):
         stack = []
         for i in range(len(string)):
             if string[i] == '#':
                 if stack: #这里重要，需要判断stack不为空，对于这种[#a#c]输入
                     stack.pop()
                 continue
             stack.append(string[i])
         return stack