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# 2022-05-18

## [344. Reverse String](https://leetcode.com/problems/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](https://en.wikipedia.org/wiki/In-place_algorithm) 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](https://en.wikipedia.org/wiki/ASCII#Printable_characters).

### Solution

```go
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](https://leetcode.com/problems/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

```go
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

```go
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)
}
```