12. Check If a String Contains All Binary Codes of Size K.cpp

/*
Check If a String Contains All Binary Codes of Size K
=====================================================

Given a binary string s and an integer k.

Return True if every binary code of length k is a substring of s. Otherwise, return False.

Example 1:
Input: s = "00110110", k = 2
Output: true
Explanation: The binary codes of length 2 are "00", "01", "10" and "11". They can be all found as substrings at indicies 0, 1, 3 and 2 respectively.

Example 2:
Input: s = "00110", k = 2
Output: true

Example 3:
Input: s = "0110", k = 1
Output: true
Explanation: The binary codes of length 1 are "0" and "1", it is clear that both exist as a substring. 

Example 4:
Input: s = "0110", k = 2
Output: false
Explanation: The binary code "00" is of length 2 and doesn't exist in the array.

Example 5:
Input: s = "0000000001011100", k = 4
Output: false

Constraints:
1 <= s.length <= 5 * 10^5
s consists of 0's and 1's only.
1 <= k <= 20

Hint #1  
We need only to check all sub-strings of length k.

Hint #2  
The number of distinct sub-strings should be exactly 2^k.
*/

class Solution
{
public:
  bool hasAllCodes(string s, int k)
  {
    unordered_set<string> substrs;
    for (int i = 0; i + k <= s.size(); ++i)
    {
      string curr = s.substr(i, k);
      substrs.insert(curr);
    }
    return (int)substrs.size() == (int)pow(2, k);
  }
};