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".

Constraints:

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

Code

class Solution:
    def reversePrefix(self, word: str, char: str) -> str:
        charIndex = word.find(char)
        pre = word[0:charIndex + 1]
        return pre[::-1] + word[charIndex + 1:]

class Solution:
    def reversePrefix(self, word: str, char: str) -> str:
        charIndex = word.find(char)
        res = ''
        l, r = 0, charIndex
        while l <= r:
            res += word[r]
            r-=1
        res +=  word[charIndex + 1:]

        return res

class Solution {
    public String reversePrefix(String word, char ch) {
        int charIndex = word.indexOf(ch);
        String pre = new StringBuilder(word.substring(0, charIndex + 1)).reverse().toString();
        return pre + word.substring( charIndex + 1);
    }
}

class Solution {
    public String reversePrefix(String word, char ch) {
        int charIndex = word.indexOf(ch);

        String prefix = reverse(word.substring(0, charIndex + 1));
        String postfix = word.substring(charIndex + 1);

        return prefix + postfix;
    }

    private String reverse(String word) {
        String res = "";

        for (int i = word.length() - 1; i >= 0; i--) {
            res += word.charAt(i);
        }

        return res;
    }
}

func reversePrefix(word string, ch byte) string {
    chIndex := findIndexInString(word, ch)
    prefix := reverse(word[0:chIndex + 1])
    postfix := word[chIndex + 1:]

    return prefix + postfix
}

func reverse(word string) string {
   var res strings.Builder
    n := len(word)

    for i := n - 1; i >= 0; i-- {
        res.WriteByte(word[i])
    }

    return res.String()
}

func findIndexInString(word string, ch byte) int {
    for i := range word {
        if word[i] == byte(ch) {
            return i
        }
    }

    return -1
}