Longest Binary Subsequence Less Than or Equal to K LeetCode solution in Java

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class Solution {
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  public int longestSubsequence(String s, int k) {
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    int z = 0;
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    // count zero
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    for (int i = 0; i < s.length(); i++) if (s.charAt(i) == '0') z++;
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    int num = 0, base = 1, len = 0;
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    // take as many ones from right as possible until they do not make the num>k
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    for (int i = s.length() - 1; i >= 0; i--) {
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      if (num + base > k) break;
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      if (s.charAt(i) == '1') {
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        num += base;
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      } else {
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        // remove already taken zeros from zeros count
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        z--;
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      }
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      base *= 2;
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      len++;
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    }
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    return len + z;
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  }
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}