1763.-longest-nice-substring.md

1763. Longest Nice Substring

class Solution:
    def longestNiceSubstring(self, s: str) -> str:
        
        n = len(s)
        
        def check(l, r):
            dit = collections.defaultdict(set)
            for i in range(l , r):
                key = s[i].lower()
                dit[key].add( s[i])

            for v in dit.values():
                if len(v) == 1:
                    return False
            return True
        ans= []
        for i in range(n + 1):
            for j in range(i):
                if check(j, i):
                    ans.append((i - j, -i , s[j:i]))
        
        ans.sort(reverse = True)
        return ans[0][-1] if ans else ""