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/**

* 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: C = 100, L = 50, XXX = 30 and III = 3.

*

* Example 5:

* Input: "MCMXCIV"

* Output: 1994

* Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

*/

public class RomanToInteger13 {

public int romanToInt(String s) {

int res = 0;

int i = 0;

while (i < s.length()) {

char c = s.charAt(i);

switch (c) {

case 'I':

if (i+1 < s.length()) {

char next = s.charAt(i+1);

if (next == 'V') {

res += 4;

i += 2;

} else if (next == 'X') {

res += 9;

i += 2;

} else {

res += 1;

i++;

}

} else {

res += 1;

i++;

}

break;

case 'V':

res += 5;

i++;

break;

case 'X':

if (i+1 < s.length()) {

char next = s.charAt(i+1);

if (next == 'L') {

res += 40;

i += 2;

} else if (next == 'C') {

res += 90;

i += 2;

} else {

res += 10;

i++;

}

} else {

res += 10;

i++;

}

break;

case 'L':

res += 50;

i++;

break;

case 'C':

if (i+1 < s.length()) {

char next = s.charAt(i+1);

if (next == 'D') {

res += 400;

i += 2;

} else if (next == 'M') {

res += 900;

i += 2;

} else {

res += 100;

i++;

}

} else {

res += 100;

i++;

}

break;

case 'D':

res += 500;

i++;

break;

case 'M':

res += 1000;

i++;

break;

default:

return 0;

}

}

return res;

}

/**

* https://leetcode.com/problems/roman-to-integer/discuss/6509/7ms-solution-in-Java.-easy-to-understand

*/

public int romanToInt2(String s) {

int nums[]=new int[s.length()];

for(int i=0;i<s.length();i++){

switch (s.charAt(i)){

case 'M':

nums[i]=1000;

break;

case 'D':

nums[i]=500;

break;

case 'C':

nums[i]=100;

break;

case 'L':

nums[i]=50;

break;

case 'X' :

nums[i]=10;

break;

case 'V':

nums[i]=5;

break;

case 'I':

nums[i]=1;

break;

}

}

int sum=0;

for(int i=0;i<nums.length-1;i++){

if(nums[i]<nums[i+1])

sum-=nums[i];

else

sum+=nums[i];

}

return sum+nums[nums.length-1];

}

}