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RomanToInt.java

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package Algorithms.string;

public class RomanToInt {

public int romanToInt(String s) {

if (s == null) {

return 0;

}

int len = s.length();

int sum = 0;

int pre = 0;

for (int i = len - 1; i >= 0; i--) {

int cur = romanTable(s.charAt(i));

if (i == len - 1) {

// 如果是在尾部，直接加上当前值

sum += cur;

} else {

// 判定当前值是不是比前一个值要小，如果小，则需要减去它

if (cur < pre) {

sum -= cur;

} else {

sum += cur;

}

}

pre = cur;

}

return sum;

}

public int romanTable(char c) {

int num = 0;

switch(c) {

case 'I':

num = 1;

break;

case 'V':

num = 5;

break;

case 'X':

num = 10;

break;

case 'L':

num = 50;

break;

case 'C':

num = 100;

break;

case 'D':

num = 500;

break;

case 'M':

num = 1000;

break;

default:

num = 0;

break;

}

return num;

}

}