# 0557. Reverse Words in a String III

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{% tab title="❓ Problem Statement" %}

> Source: [LeetCode - Reverse Words in a String III](https://leetcode.com/problems/reverse-words-in-a-string-iii/)\
> GitHub: [Solution / Performance](https://github.com/yylou/leetcode/tree/main/0557-reverse-words-in-a-string-iii)

Given a string `s`, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.
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{% tab title="✍🏻 Constraints & Example" %}
**Constraints:**

* `1 <= s.length <= 5 * 10^4`
* `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.**

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

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

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{% tabs %}
{% tab title="💡 Ideas" %}
{% hint style="info" %}

1. **Extract words** from the input string
2. **Reverse the word** then **append** to the returned string
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{% tabs %}
{% tab title="🤖 Python3" %}

```python
class Solution:
    def reverseWords(self, s: str) -> str:
        
        # ==================================================
        #  String                                          =
        # ==================================================
        # time  : O(n), n is the length of s
        # space : O(n)
        
        l, r = 0, len(s) - 1
        word, ans = '', ''
        while l <= r:
            if s[l] == ' ':
                if word: ans += self.reverse(word) + ' '
                word = ''
                l += 1
                continue
                
            word += s[l]
            l += 1
        
        if word: ans += self.reverse(word) + ' '
            
        return ans[:-1]
            
    def reverse(self, s: str) -> str:
        s, l, r = [char for char in s], 0, len(s) - 1
        while l < r:
            s[l], s[r] = s[r], s[l]
            l += 1
            r -= 1
            
        ret = ''
        for char in s: ret += char
        return ret
    
    '''
    def reverseWords(self, s: str) -> str:
        return ' '.join(x[::-1] for x in s.split())
    '''
```

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{% tab title="🤖 Java" %}

```java
class Solution {
    /**
     * @time  : O(n)
     * @space : O(n)
     */
    
    public String reverseWords(String input) {
        StringBuilder result = new StringBuilder();
        StringBuilder word = new StringBuilder();
        
        for (int i = 0; i < input.length(); i++) {
            if (input.charAt(i) != ' ') {
                word.append(input.charAt(i));
            } else {
                result.append(word.reverse());
                result.append(" ");
                word.setLength(0);
            }
        }
        
        result.append(word.reverse());
        return result.toString();
    }
}
```

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