#include <bits/stdc++.h>
using namespace std;
char firstRepeating(string &str)
{unordered_set<char> h;
for (int i=0; i<str.length(); i++)
{char c = str[i];
if (h.find(c) != h.end())
return c;
else
h.insert(c);
}
return '\0';
}
int main ()
{
string str = "geeksforgeeks";
cout << firstRepeating(str);
return 0;
}
I2luY2x1ZGUgPGJpdHMvc3RkYysrLmg+CnVzaW5nIG5hbWVzcGFjZSBzdGQ7CmNoYXIgZmlyc3RSZXBlYXRpbmcoc3RyaW5nICZzdHIpCnt1bm9yZGVyZWRfc2V0PGNoYXI+IGg7Cglmb3IgKGludCBpPTA7IGk8c3RyLmxlbmd0aCgpOyBpKyspCgkJe2NoYXIgYyA9IHN0cltpXTsKCQlpZiAoaC5maW5kKGMpICE9IGguZW5kKCkpCgkJCXJldHVybiBjOwoJCWVsc2UgCgkJCWguaW5zZXJ0KGMpOwoJfQoJcmV0dXJuICdcMCc7Cn0KaW50IG1haW4gKCkKewoJc3RyaW5nIHN0ciA9ICJnZWVrc2ZvcmdlZWtzIjsKCWNvdXQgPDwgZmlyc3RSZXBlYXRpbmcoc3RyKTsKCXJldHVybiAwOwp9Cg==