Problem

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.

Pre analysis

we can use push characted till we find ch and then reverse, followed by adding the rest of the string as it is.

Another Solution

Clean solution

/**
 * @param {string} word
 * @param {character} ch
 * @return {string}
 */
var reversePrefix = function (word, ch) {
  const index = word.indexOf(ch);
  const arr1 = word
    .split("")
    .slice(0, index + 1)
    .reverse();
  const arr2 = word.split("").slice(index + 1);
  return arr1.concat(arr2).join("");
};