Leetcode-273-Integer to English

这是一道细节题，没有什么思维量，但是写的时候要小心空格问题和零的处理。

代码如下：

class Solution {
public:
    string threeDigit(int num, map<int,string>& mp)
    {
        string str="";
        if(num==0) return str;
        if(num>=100)
        {
            str+=mp[num/100]+" "+"Hundred"+" ";
            num-=num/100*100;
        }
        if(num==0) return str;
        if(num<=20) return str+mp[num]+" ";
        str+=mp[num/10*10]+" ";
        num-=num/10*10;
        if(num!=0) str+=mp[num]+" ";
        return str;
    }
    string numberToWords(int num) {
        if(num==0) return "Zero";
        map<int,string> Digit={{0,""},{1,"Thousand"},{2,"Million"},{3,"Billion"}};
        map<int,string> mp={{1,"One"},{2,"Two"},{3,"Three"},{4,"Four"},{5,"Five"},
        {6,"Six"},{7,"Seven"},{8,"Eight"},{9,"Nine"},{10,"Ten"},{11,"Eleven"},
        {12,"Twelve"},{13,"Thirteen"},{14,"Fourteen"},{15,"Fifteen"},{16,"Sixteen"},
        {17,"Seventeen"},{18,"Eighteen"},{19,"Nineteen"},{20,"Twenty"},{30,"Thirty"},
        {40,"Forty"},{50,"Fifty"},{60,"Sixty"},{70,"Seventy"},{80,"Eighty"},{90,"Ninety"}};
        vector<int> nums;
        int cnt=0,now=0;
        while(num)
        {
            now+=(num%10)*pow(10,cnt);
            num/=10;
            cnt++;
            if(cnt==3)
            {
                nums.push_back(now);
                cnt=0;
                now=0;
            }
        }
        if(now) nums.push_back(now);
        string res;
        int n=nums.size();
        for(int i=n-1;i>=0;i--)
        {   
            string str=threeDigit(nums[i],mp);
            if(str!="")
                res+=str+Digit[i]+" ";
        }
        int k=res.size()-1;
        while(k>=0&&res[k]==' ') k--;
        return res.substr(0,k+1);
    }
};