Create tag-validator.py

kamyu104 · web-flow · commit 4e9220dac7aa · 2017-06-17T20:05:24.000+08:00
diff --git a/Python/tag-validator.py b/Python/tag-validator.py
@@ -0,0 +1,133 @@
+# Time:  O(n)
+# Space: O(n)
+
+# Given a string representing a code snippet,
+# you need to implement a tag validator to parse the code and return whether it is valid.
+# A code snippet is valid if all the following rules hold:
+#
+# 1. The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
+# 2. A closed tag (not necessarily valid) has exactly the following format :
+#    <TAG_NAME>TAG_CONTENT</TAG_NAME>. Among them, <TAG_NAME> is the start tag,
+#    and </TAG_NAME> is the end tag. The TAG_NAME in start and end tags should be the same.
+#    A closed tag is valid if and only if the TAG_NAME and TAG_CONTENT are valid.
+# 3. A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. 
+#   Otherwise, the TAG_NAME is invalid.
+# 4. A valid TAG_CONTENT may contain other valid closed tags,
+#    cdata and any characters (see note1) EXCEPT unmatched <,
+#    unmatched start and end tag, and unmatched or closed tags with invalid TAG_NAME.
+#    Otherwise, the TAG_CONTENT is invalid.
+# 5. A start tag is unmatched if no end tag exists with the same TAG_NAME,
+#    and vice versa. However, you also need to consider the issue of unbalanced when tags are nested.
+# 6. A < is unmatched if you cannot find a subsequent >.
+#    And when you find a < or </, all the subsequent characters until the next > should be
+#    parsed as TAG_NAME (not necessarily valid).
+# 7. The cdata has the following format : <![CDATA[CDATA_CONTENT]]>.
+#    The range of CDATA_CONTENT is defined as the characters between <![CDATA[ and the first subsequent ]]>.
+# 8. CDATA_CONTENT may contain any characters.
+#    The function of cdata is to forbid the validator to parse CDATA_CONTENT,
+#    so even it has some characters that can be parsed as tag (no matter valid or invalid),
+#    you should treat it as regular characters.
+#
+# Valid Code Examples:
+# Input: "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
+# Output: True
+# Explanation: 
+# The code is wrapped in a closed tag : <DIV> and </DIV>. 
+# The TAG_NAME is valid, the TAG_CONTENT consists of some characters and cdata. 
+# Although CDATA_CONTENT has unmatched start tag with invalid TAG_NAME,
+# it should be considered as plain text, not parsed as tag.
+# So TAG_CONTENT is valid, and then the code is valid. Thus return true.
+#
+# Input: "<DIV>>>  ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
+# Output: True
+# Explanation:
+# We first separate the code into : start_tag|tag_content|end_tag.
+# start_tag -> "<DIV>"
+# end_tag -> "</DIV>"
+# tag_content could also be separated into : text1|cdata|text2.
+# text1 -> ">>  ![cdata[]] "
+# cdata -> "<![CDATA[<div>]>]]>", where the CDATA_CONTENT is "<div>]>"
+# text2 -> "]]>>]"
+#
+# The reason why start_tag is NOT "<DIV>>>" is because of the rule 6.
+# The reason why cdata is NOT "<![CDATA[<div>]>]]>]]>" is because of the rule 7.
+# Invalid Code Examples:
+# Input: "<A>  <B> </A>   </B>"
+# Output: False
+# Explanation: Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.
+#
+# Input: "<DIV>  div tag is not closed  <DIV>"
+# Output: False
+#
+# Input: "<DIV>  unmatched <  </DIV>"
+# Output: False
+#
+# Input: "<DIV> closed tags with invalid tag name  <b>123</b> </DIV>"
+# Output: False
+#
+# Input: "<DIV> unmatched tags with invalid tag name  </1234567890> and <CDATA[[]]>  </DIV>"
+# Output: False
+#
+# Input: "<DIV>  unmatched start tag <B>  and unmatched end tag </C>  </DIV>"
+# Output: False
+# Note:
+# For simplicity, you could assume the input code (including the any characters mentioned above)
+# only contain letters, digits, '<','>','/','!','[',']' and ' '.
+
+class Solution(object):
+    def isValid(self, code):
+        """
+        :type code: str
+        :rtype: bool
+        """
+        def validText(s, i):
+            j = i
+            i = s.find("<", i)
+            return i != j, i
+
+        def validCData(s, i):
+            if s.find("<![CDATA[", i) != i:
+                return False, i
+            j = s.find("]]>", i)
+            if j == -1:
+                return False, i
+            return True, j+3
+
+        def parseTagName(s, i):
+            if s[i] != '<':
+                return "", i
+            j = s.find('>', i)
+            if j == -1 or not (1 <= (j-1-i) <= 9):
+                return "", i
+            tag = s[i+1:j]
+            for c in tag:
+                if not (ord('A') <= ord(c) <= ord('Z')):
+                    return "", i
+            return tag, j+1
+
+        def parseContent(s, i):
+            while i < len(s):
+                result, i = validText(s, i)
+                if result:
+                    continue
+                result, i = validCData(s, i)
+                if result:
+                    continue
+                result, i = validTag(s, i)
+                if result:
+                    continue
+                break
+            return i
+
+        def validTag(s, i):
+            tag, j = parseTagName(s, i)
+            if not tag:
+                return False, i
+            j = parseContent(s, j)
+            k = j + len(tag) + 2 
+            if k >= len(s) or s[j:k+1] != "</" + tag + ">":
+                return False, i
+            return True, k+1
+    
+        result, i = validTag(code, 0)
+        return result and i == len(code)
