LeetCode | 易学教程

Topic

Math
String

Description

https://leetcode.com/problems/roman-to-integer/

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, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 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 a roman numeral, convert it to an integer.

Example 1:

Input: s = "III"
Output: 3

Example 2:

Input: s = "IV"
Output: 4

Example 3:

Input: s = "IX"
Output: 9

Example 4:

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

Example 5:

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

Constraints:

1 <= s.length <= 15
s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
It is guaranteed that s is a valid roman numeral in the range [1, 3999].

Analysis

略

Submission

public class RomanToInteger {
	
	//方法一：我写的早期版本
	public int romanToInt1(String romanNum) {
		int sum = 0;
		int[] in = new int[romanNum.length()];
		for (int i = 0; i != in.length; i++) {
			in[i] = map(romanNum.charAt(i));
			if (i != 0) {
				if (in[i - 1] < in[i]) {
					in[i - 1] = -in[i - 1];
				}
			}
		}
		for (int t : in) {
			sum += t;
		}
		return sum;
	}

	//方法二：我写的，方法一的改进版
	public int romanToInt2(String romanNum) {
		int sum = 0, last = Integer.MAX_VALUE;

		for (int i = 0; i < romanNum.length(); i++) {
			int current = map(romanNum.charAt(i));
			sum += current;
			if (last < current)
				sum += -2 * last;
			last = current;
		}

		return sum;
	}

	private int map(char c) {
		switch (c) {
			case 'I':
				return 1;
			case 'V':
				return 5;
			case 'X':
				return 10;
			case 'L':
				return 50;
			case 'C':
				return 100;
			case 'D':
				return 500;
			case 'M':
				return 1000;
			default:
				return 0;
		}
	}

	//方法三：别人写的
	public int romanToInt3(String s) {
		int res = 0;
		for (int i = s.length() - 1; i >= 0; i--) {
			char c = s.charAt(i);
			switch (c) {
			case 'I':
				res += (res >= 5 ? -1 : 1);
				break;
			case 'V':
				res += 5;
				break;
			case 'X':
				res += 10 * (res >= 50 ? -1 : 1);
				break;
			case 'L':
				res += 50;
				break;
			case 'C':
				res += 100 * (res >= 500 ? -1 : 1);
				break;
			case 'D':
				res += 500;
				break;
			case 'M':
				res += 1000;
				break;
			}
		}
		return res;
	}

}

Test

import static org.junit.Assert.*;

import org.junit.Test;

public class RomanToIntegerTest {

	@Test
	public void test1() {
		RomanToInteger ri = new RomanToInteger();
		assertEquals(1, ri.romanToInt1("I"));
		assertEquals(5, ri.romanToInt1("V"));
		assertEquals(10, ri.romanToInt1("X"));
		assertEquals(50, ri.romanToInt1("L"));
		assertEquals(100, ri.romanToInt1("C"));
		assertEquals(500, ri.romanToInt1("D"));
		assertEquals(1000, ri.romanToInt1("M"));
		assertEquals(81, ri.romanToInt1("LXXXI"));
		assertEquals(183, ri.romanToInt1("CLXXXIII"));
		assertEquals(810, ri.romanToInt1("DCCCX"));
		assertEquals(811, ri.romanToInt1("DCCCXI"));
		assertEquals(1544, ri.romanToInt1("MDXLIV"));

		assertEquals(4, ri.romanToInt1("IV"));
		assertEquals(9, ri.romanToInt1("IX"));
		assertEquals(3, ri.romanToInt1("III"));
		assertEquals(58, ri.romanToInt1("LVIII"));
		assertEquals(1994, ri.romanToInt1("MCMXCIV"));
	}
	
	@Test
	public void test2() {
		RomanToInteger ri = new RomanToInteger();
		assertEquals(1, ri.romanToInt2("I"));
		assertEquals(5, ri.romanToInt2("V"));
		assertEquals(10, ri.romanToInt2("X"));
		assertEquals(50, ri.romanToInt2("L"));
		assertEquals(100, ri.romanToInt2("C"));
		assertEquals(500, ri.romanToInt2("D"));
		assertEquals(1000, ri.romanToInt2("M"));
		assertEquals(81, ri.romanToInt2("LXXXI"));
		assertEquals(183, ri.romanToInt2("CLXXXIII"));
		assertEquals(810, ri.romanToInt2("DCCCX"));
		assertEquals(811, ri.romanToInt2("DCCCXI"));
		assertEquals(1544, ri.romanToInt2("MDXLIV"));
		
		assertEquals(4, ri.romanToInt2("IV"));
		assertEquals(9, ri.romanToInt2("IX"));
		assertEquals(3, ri.romanToInt2("III"));
		assertEquals(58, ri.romanToInt2("LVIII"));
		assertEquals(1994, ri.romanToInt2("MCMXCIV"));
	}
	
	@Test
	public void test3() {
		RomanToInteger ri = new RomanToInteger();
		assertEquals(1, ri.romanToInt3("I"));
		assertEquals(5, ri.romanToInt3("V"));
		assertEquals(10, ri.romanToInt3("X"));
		assertEquals(50, ri.romanToInt3("L"));
		assertEquals(100, ri.romanToInt3("C"));
		assertEquals(500, ri.romanToInt3("D"));
		assertEquals(1000, ri.romanToInt3("M"));
		assertEquals(81, ri.romanToInt3("LXXXI"));
		assertEquals(183, ri.romanToInt3("CLXXXIII"));
		assertEquals(810, ri.romanToInt3("DCCCX"));
		assertEquals(811, ri.romanToInt3("DCCCXI"));
		assertEquals(1544, ri.romanToInt3("MDXLIV"));
		
		assertEquals(4, ri.romanToInt3("IV"));
		assertEquals(9, ri.romanToInt3("IX"));
		assertEquals(3, ri.romanToInt3("III"));
		assertEquals(58, ri.romanToInt3("LVIII"));
		assertEquals(1994, ri.romanToInt3("MCMXCIV"));
	}
}

来源：oschina

链接：https://my.oschina.net/jallenkwong/blog/4874677

标签

junit

java