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RomanToInt.java
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98 lines (86 loc) · 2.28 KB
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package Algorithms.string;
import java.util.HashMap;
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;
}
/*
* Solution 2: use map to solve it.
* */
public int romanToInt2(String s) {
if (s == null) {
return 0;
}
// bug 1: forget new.
HashMap<Character, Integer> map = new HashMap<Character, Integer>();
map.put('I', 1);
map.put('V', 5);
map.put('X', 10);
map.put('L', 50);
map.put('C', 100);
map.put('D', 500);
map.put('M', 1000);
int len = s.length();
int num = 0;
for (int i = len - 1; i >= 0; i--) {
int cur = map.get(s.charAt(i));
if (i < len - 1 && cur < map.get(s.charAt(i + 1))) {
num -= cur;
} else {
num += cur;
}
}
return num;
}
}