【12】Integer to Roman

按9 5 4 1一点一点减

string intToRoman(int num) {    string res="";    int c=num/1000;    res+=string(c,'M');    num-=(c*1000);    if(num>=900){res+="CM";num-=900;}    else if(num>=500){res+="D";num-=500;}    else if(num>=400){res+="CD";num-=400;}    c=num/100;    res+=string(c,'C');    num-=(c*100);    if(num>=90){res+="XC";num-=90;}    else if(num>=50){res+="L";num-=50;}    else if(num>=40){res+="XL";num-=40;}    c=num/10;    res+=string(c,'X');    num-=(c*10);    if(num>=9){res+="IX";num-=9;}    else if(num>=5){res+="V";num-=5;}    else if(num>=4){res+="IV";num-=4;}    c=num;    res+=string(c,'I');    return res;}