2022-05-18

344. Reverse String

Description

Write a function that reverses a string. The input string is given as an array of characters s.

You must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Input: s = ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:

Input: s = ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]

Constraints:

• 1 <= s.length <= 105

• s[i] is a printable ascii character.

Solution

func reverseString(s []byte) {
    for i, j := 0, len(s)-1; i < j; {
        s[i], s[j] = s[j], s[i]
        i++
        j--
    }
}

557. Reverse Words in a String III

Description

Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: s = "Let's take LeetCode contest"
Output: "s'teL ekat edoCteeL tsetnoc"

Example 2:

Input: s = "God Ding"
Output: "doG gniD" 

Constraints:

• 1 <= s.length <= 5 * 104

• s contains printable ASCII characters.

• s does not contain any leading or trailing spaces.

• There is at least one word in s.

• All the words in s are separated by a single space.

Solution

Approach #0

func reverseWord(s []rune) string {
    for i, j := 0, len(s)-1; i < j; {
        s[i], s[j] = s[j], s[i]
        i++
        j--
    }
    return string(s)
}

func reverseWords(s string) string {
    sList := strings.Split(s, " ")
    var res []string
    for _, aS := range sList {
        res = append(res, reverseWord([]rune(aS)))
    }
    return strings.Join(res, " ")
}

Approach #1

func reverseWord(s []rune) {
    for i, j := 0, len(s)-1; i < j; {
        s[i], s[j] = s[j], s[i]
        i++
        j--
    }
}

func reverseWords(s string) string {
    r := []rune(s)
    l := 0
    for i, letter := range r {
        if string(letter) == " " {
            reverseWord(r[l:i])
            l = i + 1
        }
    }
    reverseWord(r[l:])
    return string(r)
}