JSFiddle - React, Tailwind, and code Playground

JavaScript

function buildTable(a,b)
{
    var returnTable = [];
    var altChars = ["A","B","C"];
    for (i = 0; i < a; i++)
    {
        returnTable[i] = [];
        for (j = 0; j < b; j++)
        {
           returnTable[i][j] = altChars[ ( ( i * a ) + j + i ) % altChars.length];
        }
    }
return returnTable
}

console.log(buildTable(4,5))