LeetCode 2000. Reverse Prefix of Word

Given a 0-indexed string word and a character ch, reverse the segment of word that starts at index 0 and ends at the index of the first occurrence of ch (inclusive). If the character ch does not exist in word, do nothing.

• For example, if word = "abcdefd" and ch = "d", then you should reverse the segment that starts at 0 and ends at 3 (inclusive). The resulting string will be "dcbaefd".

Return the resulting string.

Example 1:

Input: word = "abcdefd", ch = "d"

Output: "dcbaefd"

Explanation: The first occurrence of "d" is at index 3. Reverse the part of word from 0 to 3 (inclusive), the resulting string is "dcbaefd".

Example 2:

Input: word = "xyxzxe", ch = "z"

Output: "zxyxxe"

Explanation: The first and only occurrence of "z" is at index 3. Reverse the part of word from 0 to 3 (inclusive), the resulting string is "zxyxxe".

Example 3:

Input: word = "abcd", ch = "z"

Output: "abcd"

Explanation: "z" does not exist in word. You should not do any reverse operation, the resulting string is "abcd".

 stringbuilder 有自定义的reverse()函数，直接用就行，就不需要自己一个一个去遍历了

easy题目，直接按照题意模拟即可；

下面是代码：

Constraints:

• 1 <= word.length <= 250

• word consists of lowercase English letters.

• ch is a lowercase English letter.

Runtime: 1 ms, faster than 47.79% of Java online submissions for Reverse Prefix of Word.

Memory Usage: 40.6 MB, less than 87.13% of Java online submissions for Reverse Prefix of Word.