problem: 0844 backspace string compare

Author: cychiu8

0844 Backspace String Compare/0844 Backspace String Compare.md

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+# 0844. Backspace String Compare
+
+* Difficulty: easy
+* Link: https://leetcode.com/problems/backspace-string-compare/
+* Topics: Array-String
+
+# Clarification
+
+1. Check the inputs and outputs
+    - INPUT: two string
+    - OUTPUT: boolean
+
+# Naive Solution
+
+### Thought Process
+
+1. 每個 string 皆從最後面開始往回看
+2. 若為 # 紀錄若遇到文字要往回走一格
+3. 比對兩個 string 當下在的文字是否一樣
+- Implement
+    
+    ```python
+    class Solution:
+        def backspaceCompare(self, s: str, t: str) -> bool:
+            sIdx = len(s)-1
+            tIdx = len(t)-1
+            sSkip = 0
+            tSkip = 0
+            while sIdx >=0 or tIdx >=0:
+                while sIdx >=0:
+                    if s[sIdx] == '#':
+                        sSkip += 1
+                        sIdx -= 1
+                    elif sSkip > 0:
+                        sSkip -= 1
+                        sIdx -= 1
+                    else:
+                        break
+                while tIdx >=0:
+                    if t[tIdx] == '#':
+                        tSkip += 1
+                        tIdx -= 1
+                    elif tSkip > 0:
+                        tSkip -= 1
+                        tIdx -= 1
+                    else:
+                        break
+                if sIdx >= 0 and tIdx >= 0 and s[sIdx] != t[tIdx]:
+                    return False
+                if (sIdx >=0 ) != (tIdx >=0):
+                    return False
+                sIdx -= 1
+                tIdx -= 1
+            return True
+    ```
+    
+
+### Complexity
+
+- Time complexity: $O(n)$
+- Space complexity:$O(1)$