Check If a String Contains All Binary Codes of Size K

Problem

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 indices 0, 1, 3 and 2 respectively.

Example 2:

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 3:

Input: s = "0110", k = 2
Output: false
Explanation: The binary code "00" is of length 2 and does not exist in the array.

Constraints:

1 <= s.length <= 5 * 10^5
s[i] is either '0' or '1'.
1 <= k <= 20

Solution (Java)

class Solution {
    public boolean hasAllCodes(String s, int k) {
        int total = (int) Math.pow(2, k);
        int start = 0;
        int end = start + k;
        Set<String> st = new HashSet<>();
        while (end <= s.length()) {
            String sbStr = s.substring(start, end);
            st.add(sbStr);
            if (st.size() == total) {
                return true;
            }
            start++;
            end++;
        }
        return false;
    }
}

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(n).