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Commit edeba98

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LeetCode problem: 13. Roman to Integer
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# 13. Roman to Integer
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Difficulty: `Easy`
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Topics: `Hash Table`, `Math`, `String`
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Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.
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```
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Symbol Value
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I 1
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V 5
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X 10
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L 50
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C 100
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D 500
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M 1000
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```
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For example, `2` is written as `II` in Roman numeral, just two ones added together. `12` is written as `XII`, which is
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simply `X + II`. The number `27` is written as `XXVII`, which is `XX + V + II`.
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Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not `IIII`.
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Instead, the number four is written as `IV`. Because the one is before the five we subtract it making four. The same
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principle applies to the number nine, which is written as `IX`. There are six instances where subtraction is used:
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* `I` can be placed before `V` (5) and `X` (10) to make 4 and 9.
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* `X` can be placed before `L` (50) and `C` (100) to make 40 and 90.
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* `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900.
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Given a roman numeral, convert it to an integer.
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**Example 1:**
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````text
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Input: s = "III"
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Output: 3
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Explanation: III = 3.
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Example 2:
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````
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**Example 2:**
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```text
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Input: s = "LVIII"
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Output: 58
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Explanation: L = 50, V= 5, III = 3.
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Example 3:
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```
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**Example 3:**
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```text
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Input: s = "MCMXCIV"
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Output: 1994
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Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
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```
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**Constraints:**
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* `1 <= s.length <= 15`
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* `s` contains only the characters (`I`, `V`, `X`, `L`, `C`, `D`, `M`).
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* It is guaranteed that `s` is a valid roman numeral in the range `[1, 3999]`.
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package com.bl.roman_to_integer;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* This is the solution to the LeetCode problem: 13. Roman to Integer
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月23日
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*/
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class Solution {
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// A map of roman numeral symbols by value.
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static final Map<Character, Integer> ROMAN_NUMERAL_SYMBOLS_BY_VALUE = new HashMap<>();
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// Initialize the map.
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static {
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('I', 1);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('V', 5);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('X', 10);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('L', 50);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('C', 100);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('D', 500);
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ROMAN_NUMERAL_SYMBOLS_BY_VALUE.put('M', 1000);
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}
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public int romanToInt(String romanNumberAsString) {
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// The sum of the roman numeral symbols.
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int sum = 0;
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// Convert the roman numeral string to a character array that we can
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// iterate over.
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final char[] characters = romanNumberAsString.toCharArray();
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// The value of the current roman numeral symbol (used in the loop).
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int currentValue;
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// The value of the previous roman numeral symbol (used in the loop).
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int previousValue = 0;
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// Iterate over the roman numeral symbols in reverse order. That way we
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// can traverse the roman numeral symbols in "ascending" order.
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for (int i = characters.length - 1; i >= 0; i--) {
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// This is the current character we're iterating over.
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final char character = characters[i];
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// Retrieve the value of the roman numeral symbol.
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currentValue = ROMAN_NUMERAL_SYMBOLS_BY_VALUE.get(character);
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// If the previous value is greater than the current value, we need
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// to subtract the current value from the sum. Otherwise, we need to
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// add the current value to the sum.
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if (previousValue > currentValue) {
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sum -= currentValue;
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} else {
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sum += currentValue;
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}
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// Set the previous value to the current value.
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previousValue = currentValue;
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}
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// Return the sum.
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return sum;
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}
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}
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package com.bl.roman_to_integer;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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/**
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* This is the test to the LeetCode problem: 13. Roman to Integer
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月23日
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*/
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@DisplayName("Roman to Integer")
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class SolutionTest {
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@Test
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@DisplayName("Example one")
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void exampleOne() {
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String s = "III";
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int expected = 3;
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assertEquals(expected, new Solution().romanToInt(s));
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}
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@Test
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@DisplayName("Example two")
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void exampleTwo() {
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String s = "LVIII";
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int expected = 58;
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assertEquals(expected, new Solution().romanToInt(s));
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}
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@Test
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@DisplayName("Example three")
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void exampleThree() {
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String s = "MCMXCIV";
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int expected = 1994;
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assertEquals(expected, new Solution().romanToInt(s));
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}
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@Test
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@DisplayName("Roman IV")
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void romanIv() {
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String s = "IV";
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int expected = 4;
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assertEquals(expected, new Solution().romanToInt(s));
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}
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@Test
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@DisplayName("Roman VII")
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void romanVii() {
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String s = "VII";
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int expected = 7;
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assertEquals(expected, new Solution().romanToInt(s));
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}
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}

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