LeetCode 0013 - Roman to Integer
# Hints
- 模拟
# 题面
Difficulty | Time Complexity Limit | Extra-Memory Complexity Limit |
---|---|---|
Medium |
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 to .
# 题意
给定一个罗马数字格式的字符串,将其转化为正整数,规则如题目所述。
# 题解
找到罗马数字的规则,然后据此模拟即可,详见代码实现。
# AC代码
class Solution {
public:
int romanToInt(string s) {
// 主循环
int res = 0;
for (int i = 0; i < s.length(); i ++) {
int num = get_number(s[i]);
if (i == s.size()-1 || num >= getNumber(s[i+1])) {
res += num;
} else {
res -= num;
}
}
// 返回
return res;
}
// 获取数值
int get_number(char ch) {
switch (ch) {
case 'I': return 1;
case 'V': return 5;
case 'X': return 10;
case 'L': return 50;
case 'C': return 100;
case 'D': return 500;
case 'M': return 1000;
}
return 0;
}
};
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