2000. Reverse Prefix of Word

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# 題目敘述

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".

# 解題思路

# Solution

class Solution {

    public String reversePrefix(String word, char ch) {

        int j = word.indexOf(ch);

        if (j != -1) {

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

        }

        return word;

    }

}