算法是一个程序员的核心竞争力,也是面试最重要的考查环节。
罗马数字包含七种字符:I,V,X,L,C,D和M,如下
字符 | 数值 |
---|---|
I | 1 |
V | 5 |
X | 10 |
L | 50 |
C | 100 |
D | 500 |
M | 1000 |
规则:
IIII=4
,MMMM=4000
除外;在线阿拉伯数字和罗马数字互相转换
https://www.onlineconversion.com/roman_numerals_advanced.htm
The input must be in the range of 1 - 4999, or I to MMMMCMXCIX.
罗马数字最大只能表示到4999。
比如输入:LVIIID,系统提示:LVIIID is not a valid input
https://www.luomashuzi.com/
使用正则表达式来判断一个给定的字符串是不是合法的罗马数字字符串:
public static boolean isRoman(String s) {return !s.isEmpty()&& s.matches("M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})");
}
将一个阿拉伯数字转换成罗马数字,显然需要考虑罗马数字的有效性问题。
public static String convertToRoman(int num) {if (num >= 5000) {return "";}String result = "";if (num >= 1000) {result = repeat("M", (int) Math.floor(1.0 * num / 1000));num %= 1000;}if (num >= 100) {result += geneBase((int) Math.floor(1.0 * num / 100), new String[]{"C", "D", "M"});num %= 100;}if (num >= 10) {result += geneBase((int) Math.floor(1.0 * num / 10), new String[]{"X", "L", "C"});num %= 10;}if (num >= 1) {result += geneBase((int) Math.floor(num), new String[]{"I", "V", "X"});}return result;
}private static String geneBase(int num, String[] arr) {String result = "";if (num >= 1 && num <= 3) {result = repeat(arr[0], num);}if (num == 4) {result = arr[0] + "" + arr[1];}if (num >= 5 && num <= 8) {result = arr[1] + "" + repeat(arr[0], num - 5);}if (num == 9) {result = arr[0] + "" + arr[2];}return result;
}/*** 重复多次*/
private static String repeat(String str, int count) {StringBuilder result = new StringBuilder();for (int i = 0; i < count; i++) {result.append(str);}return result.toString();
}
给定一个罗马数字表示的字符串,将其转换成数字,即阿拉伯数字。
注:可以假定给定的罗马数字字符串是合法的。
public static int romanToInt(String s) {int n = 0;for (int i = 0; i < s.length(); ) {char c = s.charAt(i);if (c == 'I') {if (i + 1 < s.length()) {if (s.charAt(i + 1) == 'V') {n += 4;i += 2;} else if (s.charAt(i + 1) == 'X') {n += 9;i += 2;} else {n += 1;i++;}} else {n += 1;i++;}} else if (c == 'X') {if (i + 1 < s.length()) {if (s.charAt(i + 1) == 'L') {n += 40;i += 2;} else if (s.charAt(i + 1) == 'C') {n += 90;i += 2;} else {n += 10;i++;}} else {n += 10;i++;}} else if (c == 'C') {if (i + 1 < s.length()) {if (s.charAt(i + 1) == 'D') {n += 400;i += 2;} else if (s.charAt(i + 1) == 'M') {n += 900;i += 2;} else {n += 100;i++;}} else {n += 100;i++;}} else if (c == 'V') {n += 5;i++;} else if (c == 'L') {n += 50;i++;} else if (c == 'D') {n += 500;i++;} else if (c == 'M') {n += 1000;i++;}}return n;
}
给定一个数字将其转换成Excel里面的列。
背景知识:
26 + 26 * 26 + 1
列是AAA,以此类推……最后一列是XFDpublic static String convertToTitle(int n) {if (n <= 0) {return "";}StringBuilder sb = new StringBuilder();while (n > 0) {n--;sb.append((char) (n % 26 + 'A'));n = n / 26;}return sb.reverse().toString();
}
public static int excelColumnNameToNumber(String columnName) {int sum = 0;if (columnName.equals("")) {return sum;}for (int i = 0; i < columnName.length(); i++) {sum *= 26;sum += (columnName.charAt(i) - 'A' + 1);}return sum;
}