## DEV Community

MD ARIFUL HAQUE

Posted on • Updated on

# 2000. Reverse Prefix of Word

2000. Reverse Prefix of Word

Easy

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 t*he 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:

``````class Solution {

/**
* @param String \$word
* @param String \$ch
* @return String
*/
function reversePrefix(\$word, \$ch) {
\$pos = strpos(\$word, \$ch);
if (\$pos !== false) {
\$prefix = substr(\$word, 0, \$pos + 1);
\$reversedPrefix = strrev(\$prefix);
\$rest = substr(\$word, \$pos + 1);
return \$reversedPrefix . \$rest;
}
return \$word;
}
}
``````