문제 링크 : Excel Sheet Column Title
/**
* @param {number} columnNumber
* @return {string}
*/
var convertToTitle = function(columnNumber) {
let res = "";
while (columnNumber > 0) {
columnNumber--;
res = String.fromCharCode((columnNumber % 26) + "A".charCodeAt(0)) + res;
columnNumber = Math.floor(columnNumber / 26);
}
return res;
};