Longest Happy Prefix LeetCode solution in C++

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class Solution {
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 public:
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  string longestPrefix(string s) {
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    if (s == "") return "";
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    int n = s.length();
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    int arr[n];
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    fill(arr, arr + n, 0);
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    int prevLPS = 0, i = 1;
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    while (i < n) {
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      if (s[i] == s[prevLPS]) {
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        arr[i] = prevLPS + 1;
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        i++;
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        prevLPS++;
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      } else if (prevLPS == 0) {
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        arr[i] = 0;
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        i++;
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      } else {
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        prevLPS = arr[prevLPS - 1];
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      }
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    }
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    int oplen = arr[n - 1];
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    string temp = s.substr(n - oplen, oplen);
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    return temp;
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  }
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};