plz help in my code soln bhaiya! 10 test cases are passed but n=5473578 is giving one character wrong.

[raj-khanna1]

10 test cases are passed but n=5473578 is giving one character wrong.
soln..

class Solution{
    public:
    void clm_name(long long int n,string&ans,vector<char>&alpha){
        if(n<=26){
            ans.push_back(alpha[n-1]);
            return;
        }
        long long clm_no=n/26;
        int row_no=n%26;
        clm_name(clm_no,ans,alpha);
        ans.push_back(alpha[row_no-1]);
        if(row_no==0)ans.push_back('Z');
    }
    string colName (long long int n)
    {   vector<char>alpha(26);
        int d=65;
        for(int i=0;i<26;i++)
        alpha[i]=d+i;
        string ans;
        clm_name(n,ans,alpha);
        return ans;
    }
};

[raj-khanna1]

class Solution{ public: void clm_name(long long int n,string&ans,vector<char>&alpha){ if(n<=26){ ans.push_back(alpha[n]); return; } long long clm_no=n/26; int row_no=n%26; clm_name(clm_no-1,ans,alpha); ans.push_back(alpha[row_no]); //if(row_no==0)ans.push_back('Z'); } string colName (long long int n) { vector<char>alpha(26); int d=65; for(int i=0;i<26;i++) alpha[i]=d+i; string ans; clm_name(n-1,ans,alpha); return ans; } };

now it's working but why we are subtracting -1 from the n bhaiya??