Formatted question description: https://leetcode.ca/all/2000.html

## Description

LeetCode Problem 2000.

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".


Constraints:

• 1 <= word.length <= 250
• word consists of lowercase English letters.
• ch is a lowercase English letter.

## Solution

1. find ch index
2. all chars before index -> reverse
• class Solution {
public String reversePrefix(String word, char ch) {

int pos = word.indexOf(ch);

if (pos < 0) {
return word;
}

return new StringBuilder(word.substring(0, pos + 1)).reverse().toString() + word.substring(pos + 1);
}
}

• // OJ: https://leetcode.com/problems/reverse-prefix-of-word/
// Time: O(N)
// Space: O(1)
class Solution {
public:
string reversePrefix(string s, char ch) {
int i = s.find(ch);
if (i == string::npos) return s;
reverse(begin(s), begin(s) + i + 1);
return s;
}
};

• # 2000. Reverse Prefix of Word
# https://leetcode.com/problems/reverse-prefix-of-word/

class Solution:
def reversePrefix(self, word: str, ch: str) -> str:
i = -1

for index,x in enumerate(word):
if x == ch:
i = index
break

if i == -1: return word

return word[:i + 1][::-1] + word[i + 1:]