leetcode 12. 整数转罗马数字

replace法，但是比较耗时

    public String intToRoman(int num) {
        String rawStr = firstConvert(num);
        rawStr = rawStr.replace("DCCCC", "CM");
        rawStr = rawStr.replace("CCCC", "CD");
        rawStr = rawStr.replace("LXXXX", "XC");
        rawStr = rawStr.replace("XXXX", "XL");
        rawStr = rawStr.replace("VIIII", "IX");
        rawStr = rawStr.replace("IIII", "IV");
        return rawStr;
    }

    public String firstConvert(int num) {
        Map<String, Integer> table = new HashMap<>();
        table.put("I", 1);
        table.put("V", 5);
        table.put("X", 10);
        table.put("L", 50);
        table.put("C", 100);
        table.put("D", 500);
        table.put("M", 1000);

        StringBuilder res = new StringBuilder();
        int remain = num;

        // 1000
        int M = remain / table.get("M");
        becomeStr(res, "M", M);
        remain = remain % table.get("M");

        // 500
        int D = remain / table.get("D");
        becomeStr(res, "D", D);
        remain = remain % table.get("D");

        // 100
        int C = remain / table.get("C");
        becomeStr(res, "C", C);
        remain = remain % table.get("C");

        // 50
        int L = remain / table.get("L");
        becomeStr(res, "L", L);
        remain = remain % table.get("L");

        // 10
        int X = remain / table.get("X");
        becomeStr(res, "X", X);
        remain = remain % table.get("X");

        // 5
        int V = remain / table.get("V");
        becomeStr(res, "V", V);
        remain = remain % table.get("V");

        becomeStr(res, "I", remain);

        return res.toString();
    }

    public void becomeStr(StringBuilder sb, String str, int times) {
        for (int i = 0; i < times; i++) {
            sb.append(str);
        }
    }

直接法

这题其实只要从大到小一 一 遍 历 一遍就行。

    class Solution {
    int[] values = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
    String[] symbols = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};

    public String intToRoman(int num) {
        StringBuffer roman = new StringBuffer();
        for (int i = 0; i < values.length; ++i) {
            int value = values[i];
            String symbol = symbols[i];
            while (num >= value) {
                num -= value;
                roman.append(symbol);
            }
            if (num == 0) {
                break;
            }
        }
        return roman.toString();
    }
}