12. Integer to Roman 数字转罗马串

string intToRoman(int num) {
    vector<int> sym = {'I', 'V', 'X', 'L', 'C', 'D', 'M'};
    string res;
    int i=-2;
    for(int j=0;j<3;++j) {
        i+=2;
        int n=num%10;
        if (n==5) {
            res.push_back(sym[i+1]);
        } else if (n>5) {
            if (n == 9) {
                res.push_back(sym[i+2]);
                res.push_back(sym[i]);
            } else {
                n-=5;
                for(int j=0;j<n;++j) res.push_back(sym[i]);
                res.push_back(sym[i+1]);
            }
        } else {
            if (n==4) {
                res.push_back(sym[i+1]);
                res.push_back(sym[i]);
            } else {
                for(int j=0;j<n;++j) res.push_back(sym[i]);
            }
        }
        num/=10;
    }
    while(num--) res.push_back('M');
    reverse(res.begin(), res.end());
    return res;
}

string intToRoman(int num) {
    string romanPieces[]={"","I","II","III","IV","V","VI","VII","VIII","IX",
                              "","X","XX","XXX","XL","L","LX","LXX","LXXX","XC",
                              "","C","CC","CCC","CD","D","DC","DCC","DCCC","CM",
                              "","M","MM","MMM","MMMM"};

    return romanPieces[num/1000+30]+romanPieces[(num/100)%10+20]
		+romanPieces[(num/10)%10+10]+romanPieces[num%10];
}