Getting a letter from an integer index

Question

I want to have a java method that gives me the specified index, the corresponding excel letter set, for example:

258 => IZ (last index)

30 => AD

120 => DR

56 => BD

The first method gives the correct result, but it is very dumb, and I do not like it. I tried to build a second method, which involves a little thought. I have already seen methods using String Builder or something like this, but I tried to create the method aka bestGetColumnName myself .

better 258 => IHGFEDCBAX (not normal)

better 30 => AD (OK, 2nd alphabet rounded)

better 120 => DCBAP (not normal)

better 56 => BAD (it seems that the 3rd alphabet round breaks my logic)

public String getColumnName(int index){
    String[] letters = {
        "A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R",
        "S","T","U","V","W","X","Y","Z","AA","AB","AC","AD","AE","AF","AG","AH",
        "AI","AJ","AK","AL","AM","AN","AO","AP","AQ","AR","AS","AT","AU","AV",
        "AW","AX","AY","AZ","BA","BB","BC","BD","BE","BF","BG","BH","BI","BJ",
        "BK","BL","BM","BN","BO","BP","BQ","BR","BS","BT","BU","BV","BW","BX",
        "BY","BZ","CA","CB","CC","CD","CE","CG","CH","CI","CJ","CK","CL","CM",
        "CN","CO","CP","CQ","CR","CS","CT","CU","CV","CW","CX","CY","CZ","DA",
        "DB","DC","DD","DF","DG","DH","DI","DJ","DK","DL","DM","DN","DO","DP",
        "DQ","DR","DS","DT","DU","DV","DW","DX","DY","DZ","EA","EB","EC","ED",
        "EE","EF","EG","EH","EI","EJ","EK","EL","EM","EN","EO","EP","EQ","ER",
        "ES","ET","EU","EV","EW","EX","EY","EZ","FA","FB","FC","FD","FE","FF",
        "FG","FH","FI","FJ","FK","FL","FM","FN","FO","FP","FQ","FR","FS","FT",
        "FU","FV","FW","FX","FY","FZ","GA","GB","GC","GD","GE","GF","GG","GH",
        "GI","GJ","GK","GL","GM","GN","GO","GP","GQ","GR","GS","GT","GU","GV",
        "GW","GX","GY","GZ","HA","HB","HC","HD","HE","HF","HG","HH","HI","HJ",
        "HK","HL","HM","HN","HO","HP","HQ","HR","HS","HT","HU","HV","HW","HX",
        "HY","HZ","IA","IB","IC","ID","IE","IF","IG","IH","II","IJ","IK","IL",
        "IM","IN","IO","IP","IQ","IR","IS","IT","IU","IV","IW","IX","IY","IZ"
    };

    if (index<=letters.length){
        return letters[index-1];
    }else{
        return null;
    }

}

, , , StringBuilder, , char, String integers, java version (1.5.x) , , , .

public String betterGetColumnName(int index){
    int res=0;
    String s = "";
    char h='0';

    while(index>26){ 
        res=index/26;
        h=(char)(res+64); 
        s+=h;
        index -=26;
    }
    h=(char)(index+64);
    s+=h;
    return s;
}

Answer 1

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, , , , , 26. 26 "", , . , 1 A, 26 Z 27 to AA. , , .

int input = 53;
String output = "";
while (input > 0) {
    int num = (input - 1) % 26;
    char letter = (char)(num+65);
    output = letter + output;
    input = (input-1) / 26;
}
System.out.println(output);

BA

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