Check If a String Contains All Binary Codes of Size K LeetCode solution in C++

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class Solution {
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 public:
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  bool hasAllCodes(string s, int k) {
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    int n = pow(2, k), m = s.size();
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    vector<bool> check(n, 0); // Check Array ,initially all value false;
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    int val = 0;      // Variable that will help in formation of binary to decimal
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                      // value of every substring.
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    int i = 0, j = 0; // Sliding window ponter.
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    while (j < m) {
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      val = val * 2 + (s[j] - '0'); // Form Binary ,Make it decimal.
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      if (j - i + 1 < k) // If window size is Less than k ,just j++;
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        j++;
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      else if (j - i + 1 == k) // If we hit k size.
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      {
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        check[val] = true;                          // Mark check cval true.
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        val = val - (s[i] - '0') * (pow(2, k - 1)); // Remove ith value's Calucaltion .
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        i++;                                        // Increment i
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        j++; // and Increment j to maintain size of window as k
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      }
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    }
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    for (int l = 0; l < n; l++) {
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      if (check[l] == false) // If we didn't find any value ,means that susbtring is missing
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        return false;        // Return false;
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    }
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    return true; // Return true;
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  }
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};