273. Integer to English Words

Posted 2020-11-18

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Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

Example 1:

Input: 123
Output: "One Hundred Twenty Three"

Example 2:

Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Example 4:

Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

 

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????????????????????????0-1 billion?????????

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?????????????????????billion????????????????????? million??????????????????thousand hundred?????????

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????????????????????????3???0?????????????????????

????????????????????????unit ???hash map????????????????????????0?????????????????????????????????

??????1-9??? 10-19??? 20??? 30??? 40??? 50??? 60??? 70 ???80??? 90????????????

???num?????????1000?????????????????????3????????????????????????????????????????????????????????????count?????????????????????

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class Solution {
public:
    string numberToWords(int num) {
        unordered_map<int,string> dict ={
            {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"}
        };
        unordered_map<int,string> unit = {{0, ""},{1, " Thousand"}, {2, " Million"}, {3," Billion"}};
        string ret = "";
        int count = 0;
        if(num == 0)
            return "Zero";
        while(num > 0){
            int cur = num % 1000;
            if(cur != 0){
                string wn = toWords(cur, dict);
                wn += unit[count];
                if(ret.size() != 0){
                    ret = " "+ret;
                }
                ret = wn + ret;
            }
            count++;
            num /= 1000;
        }
        return ret;
        
    }
private:
    string toWords(int n, unordered_map<int, string> &m){
        string ret;
        int h = n/100;
        if(h != 0)
            ret = m[h] + " Hundred";
        n %= 100;
        if(n == 0)
            return ret;
        if(m.count(n)){
            if(ret.size() != 0)
                ret += " ";
            ret += m[n];
        }else{
            int t = n/10;
            if(t != 0){
                if(ret.size() != 0)
                    ret += " ";
                ret += m[t*10];
            }
            int d = n%10;
            if(d != 0){
                if(ret.size() != 0)
                    ret += " ";
                ret += m[d];
            }
        }
        return ret;
    }
};