616. Add Bold Tag in String

You are given a string s and an array of strings words.

You should add a closed pair of bold tag <b> and </b> to wrap the substrings in s that exist in words.

• If two such substrings overlap, you should wrap them together with only one pair of closed bold-tag.
• If two substrings wrapped by bold tags are consecutive, you should combine them.

Return s after adding the bold tags.

Example 1:

Input: s = "abcxyz123", words = ["abc","123"]
Output: "<b>abc</b>xyz<b>123</b>"
Explanation: The two strings of words are substrings of s as following: "abcxyz123".
We add <b> before each substring and </b> after each substring.

Example 2:

Input: s = "aaabbb", words = ["aa","b"]
Output: "<b>aaabbb</b>"
Explanation: 
"aa" appears as a substring two times: "aaabbb" and "aaabbb".
"b" appears as a substring three times: "aaabbb", "aaabbb", and "aaabbb".
We add <b> before each substring and </b> after each substring: "<b>a<b>a</b>a</b><b>b</b><b>b</b><b>b</b>".
Since the first two <b>'s overlap, we merge them: "<b>aaa</b><b>b</b><b>b</b><b>b</b>".
Since now the four <b>'s are consecutive, we merge them: "<b>aaabbb</b>".

Constraints:

• 1 <= s.length <= 1000
• 0 <= words.length <= 100
• 1 <= words[i].length <= 1000
• s and words[i] consist of English letters and digits.
• All the values of words are unique.

解法

https://www.youtube.com/watch?v=WXb3ItOlRfQ 

找出每个字符是否需要加bold，如果是，那么那个字符对应的value就是true, 然后把连在一起的true的字符放在bold里面就可以了