Easy, Intuitive - Beats 100%
\nclass Solution {\n    public String shortestBeautifulSubstring(String s, int k) {\n        if (s.replaceAll("0", "").length() < k) {\n            return "";\n
```\nclass Solution {\n    public String shortestBeautifulSubstring(String s, int k) {\n        if (s.replaceAll("0", "").length() < k) {\n            return "";\n        }\n        int start = 0;\n        String res = "";\n        int count = 0;\n        for (int end = 0; end < s.length(); end++) {\n            if (s.charAt(end) == \'1\') {\n                count++;\n            }\n            while (count >= k) {\n                if (res.length() == 0 || end - start + 1 < res.length() || end - start + 1 == res.length() && s.substring(start, end + 1).compareTo(res) < 0) {\n                    res = s.substring(start, end + 1);\n                }\n                if (s.charAt(start) == \'1\') {\n                    count--;\n                }\n                start++;\n            }\n        }\n        \n        return res;\n    }\n}\n\n//tc: O(n ^ 2)\n//sc: O(n)\n```
['Sliding Window', 'Java']