Coding

2000. Reverse Prefix of Word

2024-05-01 2 min read
#Two Pointers#String
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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;
    }
}
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