Count Sorted Vowel Strings LeetCode solution in C++

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// Solution 01:
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class Solution {
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 public:
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  int countVowelStrings(int n) {
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    int a = 1, e = 1, i = 1, o = 1, u = 1;
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    while (--n) {
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      o += u;
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      i += o;
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      e += i;
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      a += e;
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    }
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    return a + e + i + o + u;
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  }
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};
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// Solution 02:
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class Solution {
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 public:
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  int countVowelStrings(int n) {
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    vector<int> dp(5, 1);
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    int ans = 0;
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    while (--n) {
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      for (int i = 3; i >= 0; i--) {
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        dp[i] += dp[i + 1];
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      }
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    }
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    for (auto x : dp) ans += x;
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    return ans;
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  }
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};