_591.java

package com.fishercoder.solutions;

import java.util.ArrayDeque;
import java.util.Deque;

/**
 * 591. Tag Validator
 *
 * 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 ' '.
 */
public class _591 {

    /**Credit: https://discuss.leetcode.com/topic/91300/java-solution-use-startswith-and-indexof*/
    public boolean isValid(String code) {
        Deque<String> stack = new ArrayDeque<>();
        for (int i = 0; i < code.length(); ) {
            if (i > 0 && stack.isEmpty()) {
                return false;
            }
            if (code.startsWith("<![CDATA[", i)) {
                int j = i + 9;//"<![CDATA[" length is 9
                i = code.indexOf("]]>", j);
                if (i < 0) {
                    return false;
                }
                i += 3;//"]]>" length is 3
            } else if (code.startsWith("</", i)) {
                int j = i + 2;
                i = code.indexOf(">", j);
                if (i < 0 || i == j || i - j > 9) {
                    return false;
                }
                for (int k = j; k < i; k++) {
                    if (!Character.isUpperCase(code.charAt(k))) {
                        return false;
                    }
                }
                String s = code.substring(j, i++);
                if (stack.isEmpty() || !stack.pop().equals(s)) {
                    return false;
                }
            } else if (code.startsWith("<", i)) {
                int j = i + 1;
                i = code.indexOf(">", j);
                if (i < 0 || i == j || i - j > 9) {
                    return false;
                }
                for (int k = j; k < i; k++) {
                    if (!Character.isUpperCase(code.charAt(k))) {
                        return false;
                    }
                }
                String s = code.substring(j, i++);
                stack.push(s);
            } else {
                i++;
            }
        }
        return stack.isEmpty();
    }

}