[#83][프로그래머스][입문] 다항식 더하기

function solution(polynomial) {
  polynomial = polynomial.split(' ').filter((e) => e !== '+'); 
  let xNum = 0;
  let num = 0;
  polynomial.forEach((e) => {
      if (e.includes('x')) {
          const x = e.split('x');
          if (x[0] === '') xNum++;
          if (x[0] !== '') xNum += Number(x[0]);
      }
      
      if (!e.includes('x')) num += Number(e);
  })
  
  if (xNum !== 0 && num !== 0) return xNum === 1 ? `x + ${num}` : `${xNum}x + ${num}`;
  if (xNum !== 0 && num === 0) return xNum === 1 ? 'x' : `${xNum}x`;
  if (xNum === 0 && num !== 0) return `${num}`;
  if (xNum === 0 && num === 0) return '0';
}