13.roman-to-integer.java

/*
 * @lc app=leetcode id=13 lang=java
 *
 * [13] Roman to Integer
 *
 * https://leetcode.com/problems/roman-to-integer/description/
 *
 * algorithms
 * Easy (51.58%)
 * Total Accepted:    391.1K
 * Total Submissions: 752.6K
 * Testcase Example:  '"III"'
 *
 * 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 a roman numeral, convert it to an integer. Input is guaranteed to be
 * within the range from 1 to 3999.
 *
 * Example 1:
 *
 *
 * Input: "III"
 * Output: 3
 *
 * Example 2:
 *
 *
 * Input: "IV"
 * Output: 4
 *
 * Example 3:
 *
 *
 * Input: "IX"
 * Output: 9
 *
 * Example 4:
 *
 *
 * Input: "LVIII"
 * Output: 58
 * Explanation: L = 50, V= 5, III = 3.
 *
 *
 * Example 5:
 *
 *
 * Input: "MCMXCIV"
 * Output: 1994
 * Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
 *
 */
class Solution {
  public int romanToInt(String s) {
    int sum = 0;
    int len = s.length();

    for (int i = 0; i < len; i++) {
      char ch = s.charAt(i);
      if (ch == 'I') sum += 1;
      if (ch == 'V') sum += 5;
      if (ch == 'X') sum += 10;
      if (ch == 'L') sum += 50;
      if (ch == 'C') sum += 100;
      if (ch == 'D') sum += 500;
      if (ch == 'M') sum += 1000;
    }

    if (s.indexOf("IV") != -1 || s.indexOf("IX") != -1) sum -= 2;
    if (s.indexOf("XL") != -1 || s.indexOf("XC") != -1) sum -= 20;
    if (s.indexOf("CD") != -1 || s.indexOf("CM") != -1) sum -= 200;

    return sum;
  }
}