Leetcode298 weekly race record

T3- Less than or equal to K The longest binary subsequence of

Ideas

The form of the optimal solution ： Maximum length is m = $\lfloor lo{g}_{2}k\rfloor +1$ Sequence + Put together the front All the leading 0. So find out as soon as possible from the back to the front m Bit less than or equal to k, In order to make the splicing leading 0 As much as possible .
If s Long for m The suffix of is less than or equal to k, Then the final answer is to use the suffix to splice all the preceding leading words 0; otherwise , Long for m The last digit of the suffix must be 1, So it is m-1 The suffix corresponds to a binary digit <k. It is the same as all the previous leads 0 Splicing

class Solution {
    
public:
    int longestSubsequence(string s, int k) {
    
        int count = 0;
        int m = 32 - __builtin_clz(k);;
        if(s.length() < m) return s.length();
        for(int i = 0;i<s.length() - m;i++) if(s[i]== '0') count++;
        long long temp = 0;
        //for(int i = s.length() - 1;i>=s.length() - m;i--) temp = (long long)(s[i] - '0') << ((s.length() - i));
        temp =  stoi(s.substr(s.length() - m), nullptr, 2);
        if(temp > (long long)k) return  count + m - 1;
        return count  + m;
    }
};