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"title": "Vowels of All Substrings",
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"content": "<p>Given a string <code>word</code>, return <em>the <strong>sum of the number of vowels</strong> (</em><code>'a'</code>, <code>'e'</code><em>,</em> <code>'i'</code><em>,</em> <code>'o'</code><em>, and</em> <code>'u'</code><em>)</em> <em>in every substring of </em><code>word</code>.</p>\n\n<p>A <strong>substring</strong> is a contiguous (non-empty) sequence of characters within a string.</p>\n\n<p><strong>Note:</strong> Due to the large constraints, the answer may not fit in a signed 32-bit integer. Please be careful during the calculations.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> word = "aba"\n<strong>Output:</strong> 6\n<strong>Explanation:</strong> \nAll possible substrings are: "a", "ab", "aba", "b", "ba", and "a".\n- "b" has 0 vowels in it\n- "a", "ab", "ba", and "a" have 1 vowel each\n- "aba" has 2 vowels in it\nHence, the total sum of vowels = 0 + 1 + 1 + 1 + 1 + 2 = 6. \n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> word = "abc"\n<strong>Output:</strong> 3\n<strong>Explanation:</strong> \nAll possible substrings are: "a", "ab", "abc", "b", "bc", and "c".\n- "a", "ab", and "abc" have 1 vowel each\n- "b", "bc", and "c" have 0 vowels each\nHence, the total sum of vowels = 1 + 1 + 1 + 0 + 0 + 0 = 3.\n</pre>\n\n<p><strong>Example 3:</strong></p>\n\n<pre>\n<strong>Input:</strong> word = "ltcd"\n<strong>Output:</strong> 0\n<strong>Explanation:</strong> There are no vowels in any substring of "ltcd".\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= word.length <= 10<sup>5</sup></code></li>\n\t<li><code>word</code> consists of lowercase English letters.</li>\n</ul>\n",
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"code": "class Solution {\npublic:\n long long countVowels(string word) {\n \n }\n};",
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"hints": [
"Since generating substrings is not an option, can we count the number of substrings a vowel appears in?",
"How much does each vowel contribute to the total sum?"
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