topic
Roman numeral characters comprising the following seven: I, V, X, L, C, D and M.
Numerical character
the I. 1
V. 5
X-10
L 50
C 100
D 500
M 1000
, for example, 2 written as Roman numerals II, namely 1.12 written as two parallel XII, namely X + II. 27 written as XXVII, namely XX + V + II.Typically, small numbers of Roman numerals to the right in large numbers. But there are exceptions, for example, do not write 4 IIII, but IV. In the left number 5 number 1, the number of large numbers equal to the value represented by a reduced number 5 obtained 4. Likewise, the number 9 is represented as IX. This special rule applies only to the following six cases:
I may be on the left V (5) and X (10), and to represent 4 and 9.
X L can be placed on the left (50) and C (100), and 40 and 90 are represented.
C may be placed on D (500) and M (1000) to the left, to 400 and 900 represent.
Given a Roman numeral, to convert it to an integer. To ensure that the input is in the range of 1 to 3999.Example 1:
Input: "III"
Output: 3
Example 2:Input: "IV"
Output: 4
Example 3:Enter: "IX"
Output: 9
Example 4:Input: "LVIII"
Output: 58
explains: L = 50, V = 5 , III = 3.
Example 5:Enter: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90, IV = 4.
Thinking
That is to say that six cases, only the current value is less than those of the latter, only subtraction of the former, it is just a time and a contrast of characters on the line, other cases are additions
Code
. 1 class Solution { 2 public : . 3 int romanToInt ( String S) { . 4 int Chang = s.size (); . 5 int SUM = 0 , index = 0 ; . 6 for (index = 0 ;; index ++ ) { . 7 IF (index chang- == . 1 ) { . 8 SUM + = GetSum (S [index]); // index careful not written chang, chang because of overflow . 9 BREAK ; 10 } . 11 the else { 12 is if(getsum(s[index])<getsum(s[index+1])) 13 sum-=getsum(s[index]); 14 else 15 sum+=getsum(s[index]); 16 } 17 18 } 19 20 return sum; 21 } 22 int getsum(char c){ 23 int num; 24 switch(c){ 25 case 'I':num=1; 26 break; 27 case 'V':num=5; 28 break; 29 case 'X':num=10; 30 break; 31 case 'L':num=50; 32 break; 33 case 'C':num=100; 34 break; 35 case 'D':num=500; 36 break; 37 case 'M':num=1000; 38 break; 39 40 } 41 return num; 42 } 43 44 45 };
Interpreted code
22-42 line with a function to assign to each Roman numeral, followed by the value of this function to call each letter, and finally return of a call that is num.
chang 3-21 trip is to determine the length of the input Roman characters, sum is the total value, index is now subscript character position
7-8 when the index line is the last position, nor the value on the right, the left and right without comparison value of the size, so coupled directly to s [index]
11 is the case when the line if not the last character
12-13 line first determines whether the value is less than the value of the right to the left, less than then it subtracts the value of the left
14-15 rows to the left of the value is greater than the right value, then it would add value to the left
return sum 20 returns the last row is the sum of the braces 21 at this time is that the first row line 3, because the next function is the custom, the first row belonging to class solution.
reward
s.size, when s is a string type, length is acquired
Using custom functions
Syntax need to wrap switch case statement, because this deficiency found themselves, such as single quotes after the case, and the case colon
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Original title link
13. Roman numerals to Integer