<p>A <strong>sentence</strong> is a string of single-space separated words where each word consists only of lowercase letters.</p>

<p>A word is <strong>uncommon</strong> if it appears exactly once in one of the sentences, and <strong>does not appear</strong> in the other sentence.</p>

<p>Given two <strong>sentences</strong> <code>s1</code> and <code>s2</code>, return <em>a list of all the <strong>uncommon words</strong></em>. You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s1 = &quot;this apple is sweet&quot;, s2 = &quot;this apple is sour&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">[&quot;sweet&quot;,&quot;sour&quot;]</span></p>

<p><strong>Explanation:</strong></p>

<p>The word <code>&quot;sweet&quot;</code> appears only in <code>s1</code>, while the word <code>&quot;sour&quot;</code> appears only in <code>s2</code>.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s1 = &quot;apple apple&quot;, s2 = &quot;banana&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">[&quot;banana&quot;]</span></p>
</div>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s1.length, s2.length &lt;= 200</code></li>
	<li><code>s1</code> and <code>s2</code> consist of lowercase English letters and spaces.</li>
	<li><code>s1</code> and <code>s2</code> do not have leading or trailing spaces.</li>
	<li>All the words in <code>s1</code> and <code>s2</code> are separated by a single space.</li>
</ul>

class Solution {
 public:
  std::vector<std::string> uncommonFromSentences(std::string s1,
                                                 std::string s2) {
    std::unordered_map<std::string_view, int> wordToCounts;
    const char SPACE = ' ';

    int currentWordStart = 0;
    for (int i = 1; i <= s1.size(); i++) {
      if (i == s1.size() || s1[i] == SPACE) {
        const std::string_view word(s1.cbegin() + currentWordStart,
                                    s1.cbegin() + i);
        wordToCounts[word]++;
        currentWordStart = i + 1;
      }
    }

    currentWordStart = 0;
    for (int i = 1; i <= s2.size(); i++) {
      if (i == s2.size() ||s2[i] == SPACE) {
        const std::string_view word(s2.cbegin() + currentWordStart,
                                    s2.cbegin() + i);
        wordToCounts[word]++;
        currentWordStart = i + 1;
      }
    }

    std::vector<std::string> result;

    for (const auto& wordToCount : wordToCounts) {
      const std::string_view& word = wordToCount.first;
      const int count = wordToCount.second;

      if (count == 1) {
        result.emplace_back(word);
      }
    }

    return result;
  }
};
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