LeetCode 12. Integer to Roman-优快云博客

本文链接：https://blog.youkuaiyun.com/Allenlzcoder/article/details/80708332

本文提供了两种将整数转换为罗马数字的方法。第一种方法使用了unordered_set和unordered_map来存储关键数值及其对应的罗马字符，通过循环计算每一位的数值并拼接结果字符串。第二种方法则通过预定义的字符数组和数值数组，逐位处理并将结果字符串拼接起来。

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LeetCode 12. Integer to Roman

Solution1：我的答案
好慢啊。。。

class Solution {
public:
    string intToRoman(int num) {
        unordered_set<int> key = {1, 5, 10, 50, 100, 500, 1000, 4, 9, 40, 90, 400, 900};
        unordered_map<int, string> key_value = {{1, "I"},
                                                {5, "V"}, 
                                                {10, "X"}, 
                                                {50, "L"}, 
                                                {100, "C"}, 
                                                {500, "D"}, 
                                                {1000, "M"}, 
                                                {4, "IV"}, 
                                                {9, "IX"}, 
                                                {40, "XL"}, 
                                                {90, "XC"}, 
                                                {400, "CD"},
                                                {900, "CM"}
                                               };//错落有致~
        string res = "";
        int base = 1, temp = 0;
        while (num) {
            temp = num % 10;
            temp *= base;
            if (key.find(temp) != key.end())
                res = key_value[temp] + res;
            else {
                if (temp < 5 * base) {
                    for (int i = 0; i < temp/base; i++)
                        res = key_value[base] + res;
                } else {
                    for (int i = 0; i < temp/base - 5; i++)
                        res = key_value[base] + res;
                    res = key_value[5 * base] + res;
                }
            }
            num /= 10;
            base *= 10;
        }
        return res;
    }
};

Solution2：
参考网址：http://www.cnblogs.com/grandyang/p/4123374.html
这样更快一些

class Solution {
public:
    string intToRoman(int num) {
        string res = "";
        char roman[] = {'M', 'D', 'C', 'L', 'X', 'V', 'I'};
        int value[] = {1000, 500, 100, 50, 10, 5, 1};

        for (int n = 0; n < 7; n += 2) {
            int x = num / value[n];
            if (x < 4) {
                for (int i = 1; i <= x; ++i) res += roman[n];
            } else if (x == 4) res = res + roman[n] + roman[n - 1];
            else if (x > 4 && x < 9) {
                res += roman[n - 1];
                for (int i = 6; i <= x; ++i) res += roman[n];
            }
            else if (x == 9) res = res + roman[n] + roman[n - 2];
            num %= value[n];            
        }
        return res;
    }
};