758. Bold Words in String

Given a set of keywords words and a string S , make all appearances of all keywords in S bold. Any letters between <b> and </b> tags become bold.

The returned string should use the least number of tags possible, and of course the tags should form a valid combination.

For example, given that words = ["ab", "bc"] and S = "aabcd" , we should return "a<b>abc</b>d" . Note that returning "a<b>a<b>b</b>c</b>d" would use more tags, so it is incorrect.

Note:

1. words has length in range [0, 50] .
2. words[i] has length in range [1, 10] .
3. S has length in range [0, 500] .
4. All characters in words[i] and S are lowercase letters.