leetcode 12. Integer to Roman（java）_综合

问题描述

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

I can be placed before V (5) and X (10) to make 4 and 9.
X can be placed before L (50) and C (100) to make 40 and 90.
C can be placed before D (500) and M (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: 3
Output: "III"

Example 2:

Input: 4
Output: "IV"

Example 3:

Input: 9
Output: "IX"

Example 4:

Input: 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.

Example 5:

Input: 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

解题思路

1.根据题意，罗马数字及其对应的数字分别是："M"-1000, "CM"-900, "D"-500, "CD"-400, "C"-100, "XC"-90, "L"-50, "XL"-40, "X"-10, "IX"-9, "V"-5, "IV"-4, "I"-1。

2.创立StringBuilder sb，循环迭代num判断其值所处的区间，并将区间值的下限对应的字符串拼接到sb,并将num值减去其当前区间值所处的下限。

代码(java版）


import java.util.Scanner;public class Solution {public static void main(String[] args) {Scanner in=new Scanner(System.in);int input=in.nextInt();System.out.println(new Solution().intToRoman(input));}public String intToRoman(int num) {StringBuilder sb=new StringBuilder();while(num!=0) {if(num>=1000) {sb.append("M");num-=1000;}else if(num>=900) {sb.append("CM");num-=900;}else if(num>=500) {sb.append("D");num-=500;}else if(num>=400) {sb.append("CD");num-=400;}else if(num>=100) {sb.append("C");num-=100;}else if(num>=90) {sb.append("XC");num-=90;}else if(num>=50) {sb.append("L");num-=50;}else if(num>=40) {sb.append("XL");num-=40;}else if(num>=10) {sb.append("X");num-=10;}else if(num>=9) {sb.append("IX");num-=9;}else if(num>=5) {sb.append("V");num-=5;}else if(num>=4) {sb.append("IV");num-=4;}else {sb.append("I");num-=1;}}return sb.toString();}  	
}