```
class Solution {
public:
string convertToTitle(int n) {
string res;
const int maxlen = 1000;
char tmpchar[maxlen];
memset(tmpchar, 0, sizeof(tmpchar));
long long b = 26;
int tmpcharidx = 0;
while(n > 0){
int r = n % 26;
if(r == 0){
tmpchar[tmpcharidx++] = 'Z';
n -= 26;
}
else{
tmpchar[tmpcharidx++] = 'A' + r - 1;
n -= r;
}
n /= 26;
}
for(int k = tmpcharidx - 1; k >= 0; --k){
res += tmpchar[k];
}
return res;
}
};
```

2ms solution