Simple go solution
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```golang []\nfunc shortestBeautifulSubstring(s string, k int) string {\n    l := len(s)\n    count:=0\n    ans:=""\n    \n    for i,j:=l-1,l-1;i>=0;i--{\n        if s[i]==\'1\'{\n            count++\n        }\n  \n        for i<j&&(count>k || s[j]==\'0\'){\n            if s[j]==\'1\'{\n                count--\n            }\n            j--\n        }\n\n        if count ==k{\n            ans = minValue(ans,s[i:j+1])\n        }\n\n    }\n   \n    return ans\n}\n\nfunc minValue(s1,s2 string)string{\n    if s1==""{\n        return s2\n    }\n    if len(s1)<len(s2){\n        return s1\n    }else if len(s1)>len(s2){\n        return s2\n    }\n\n    for i:=0;i<len(s1);i++{\n        if s1[i]-\'0\'< s2[i]-\'0\' {\n            return s1\n        }else if s1[i]-\'0\'> s2[i]-\'0\'{\n            return s2\n        }\n    }\n\n    return s1\n}\n```
['Go']