var read = require('readline').createInterface({ input: process.stdin, output: process.stdout }); var obj; var inLine = []; read.on('line', function(input){inLine.push(input);}); read.on('close', function(){ obj = init(inLine); myerr("-----start-----"); var start = new Date(); Main(); var end = new Date() - start; myerr("----- end -----"); myerr("time : " + (end) + "ms"); myerr("memory : " + Math.round(process.memoryUsage().heapTotal / 1024) + "KB"); }); function nextInt(){return myconv(next(),1);} function nextStrArray(){return myconv(next(),2);} function nextIntArray(){return myconv(next(),4);} function nextCharArray(){return myconv(next(),6);} function next(){return obj.next();} function hasNext(){return obj.hasNext();} function init(input){ var returnObj = { list : input, index : 0, max : input.length, hasNext : function(){return (this.index < this.max);}, next : function(){if(!this.hasNext()){throw "ArrayIndexOutOfBoundsException これ以上ないよ";}else{var returnInput = this.list[this.index];this.index++;return returnInput;}} }; return returnObj; } function myout(s){console.log(s);} function myerr(s){console.error("debug:" + require("util").inspect(s,false,null));} //[no]要素の扱い。数値型 //不明値、異常時:引数そのまま返す 1:数値へ変換 //2:半角SPで分割 4:半角SPで分割し、数値配列へ //6:1文字で分割 7:1文字で分割し、数値配列へ //8:半角SPで結合 9:改行で結合 0:文字なしで結合 function myconv(i,no){try{switch(no){case 1:return parseInt(i);case 2:return i.split(" ");case 4:return i.split(" ").map(Number);case 6:return i.split("");case 7:return i.split("").map(Number);case 8:return i.join(" ");case 9:return i.join("\n");case 0:return i.join("");default:return i;}}catch(e){return i;}} function Main(){ var N = nextInt(); var list = nextIntArray(); list.sort(function(a,b){ return a - b; }); var diff = list[1] - list[0]; for(var i = 0; i < N - 1; i++){ if(list[i] == list[i + 1] || list[i + 1] - list[i] != diff){ myout("NO"); return; } } myout("YES"); }