2000-ReversePrefixOfWord.go

package main

// 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.

import "fmt"

func reversePrefix(word string, ch byte) string {
    arr, start, end := []byte(word), 0, 0
    // 找到第一个出现在 ch 
    for i, v := range arr {
        if v == ch {
            end = i
            break
        }
    }
    for start < end {
        arr[start], arr[end] = arr[end], arr[start] // 交换字符串
        start++
        end--
    }
    return string(arr)
}

func main() {
    // 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".
    fmt.Println("abcdefd => ", reversePrefix("abcdefd", 'd')) // "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".
    fmt.Println("xyxzxe => ", reversePrefix("xyxzxe", 'z')) // "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".
    fmt.Println("abcd => ", reversePrefix("abcd", 'z')) // "abcd"
}