规则如下

image.png

限制

本次实现了3999及以下的数字转换。

具体代码

function convert(num) {

  //最大数字是3999,且为整数
  var romanNum = ['I','V','X','L','C','D','M'];
  var strNum = String(num);
  var arrNum = strNum.split("");
  var len = arrNum.length;
  var roman = '';

  for (var i = 0; i < len; i++) {
    var everyNum = Number(arrNum[i]);
    if (everyNum < 4) {
      for(var j = 0; j < Number(arrNum[i]); j++) {
        roman += romanNum[(len-i-1)*2];
      } 
    } else if (everyNum === 4) {
      roman += romanNum[(len-i-1)*2] + romanNum[(len-i-1)*2+1];
    } else if (everyNum === 5) {
      roman += romanNum[(len-i-1)*2+1];
    } else if (everyNum > 5 && everyNum <= 8) {
        roman += romanNum[(len-i-1)*2+1];
      for(var k = 0; k < Number(arrNum[i]) - 5; k++) {
        roman += romanNum[(len-i-1)*2];
      } 
    } else if (everyNum === 9) {
      roman += romanNum[(len-i-1)*2] + romanNum[(len-i)*2];
    }
  }
  
  return roman;
}

convert(9);

待改进

功能是实现了，但代码过于繁琐。。。一点都不优雅