leetcode 273

问题

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

Example 1:

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Input: 123
Output: "One Hundred Twenty Three"

Example 2:

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

Example 3:

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

Example 4:

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

分析

根据数字范围，最大的数字是 4'294'967'295，然后根据每三位为一组进行解析即可。

代码

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class Solution {
public:
    const string ones[10] = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
    const string tenplus[10] = {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    const string tens[10] = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    const string hundreds = "Hundred";
    const string q[4] = {"", "Thousand", "Million", "Billion"};
    string numberToWordsLess100(int num) {
        string ret;
        int x = num/100;
        int y = num%100;
        if (x!=0) {
            ret += ones[x] + " " + hundreds;
        }
        if (y == 0) return ret;
        if (y < 10) {
            if (ret.size() != 0) ret += " ";
            ret += ones[y];
        } else if (y < 20) {
            if (ret.size() != 0) ret += " ";
            ret += tenplus[y-10];
        } else {
            int k = y/10;
            if (ret.size() != 0) ret += " ";
            ret += tens[k];
            y = y%10;
            if (y != 0) {
                if (ret.size() != 0) ret += " ";
                ret += ones[y];
            }
        }
        return ret;
    }
    string numberToWords(int num) {
        if (num == 0) return "Zero";
        vector<int> nums;
        while (num > 0) {
            nums.push_back(num%1000);
            num /= 1000;
        }
        string ans;
        for (int i = nums.size()-1; i >= 0; --i) {
            if (nums[i] != 0) {
                if (ans.size() != 0) ans += " ";
                ans += numberToWordsLess100(nums[i]);
                if (i != 0) {
                    ans += " " + q[i];
                }
            }
        }
        return ans;
    }
};