LeetCode 2311. Longest Binary Subsequence Less Than or Equal to K

class Solution {
public:
    int longestSubsequence(string s, int k) {
        int n = s.size(), m = 32 - __builtin_clz(k);
        if (n < m) return n;
        int ans = stoi(s.substr(n - m), nullptr, 2) <= k ? m : m - 1;
        return ans + count(s.begin(), s.end() - m, '0');
    }
};