LeetCode 788. Rotated Digits (旋转数字)

X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X.  Each digit must be rotated - we cannot choose to leave it alone.

A number is valid if each digit remains a digit after rotation. 0, 1, and 8 rotate to themselves; 2 and 5 rotate to each other; 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number and become invalid.

Now given a positive number N, how many numbers X from 1 to N are good?

Example:
Input: 10
Output: 4
Explanation: 
There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.

Note:

  • N  will be in range [1, 10000]

 


 

题目标签:String

  题目给了我们一个N, 让我们找出从 1 到 N 中有几个 good number。Good Number 是每一个digit 都可以旋转,然后旋转后 与 旋转前 是不同的 数字。

  利用HashMap 把 0,1,8,2,5,6,9 这些可以旋转的数字存入保存。

  之后利用Map来检查数字的每一个 digit 是否可以旋转,当旋转完之后的新数字 要与 旧数字 不同,才可以算。

  具体请看code。

 

 

  

  

Java Solution:

Runtime beats  23.35% 

完成日期:05/11/2018

关键词:HashMap

关键点:把可以旋转的digit存入map

 1 class Solution 
 2 {
 3     public int rotatedDigits(int N) 
 4     {
 5         int count = 0;
 6         HashMap<Integer, Integer> map = new HashMap<>();
 7         
 8         map.put(0, 0);
 9         map.put(1, 1);
10         map.put(8, 8);
11         map.put(2, 5);
12         map.put(5, 2);
13         map.put(6, 9);
14         map.put(9, 6);
15         
16 
17         for(int i=1; i<=N; i++)
18         {
19             int number = i;
20             int newNumber = 0;
21             int m = 1;
22             
23             while(number > 0)
24             {
25                 int digit = number % 10;     // get the digit
26 
27                 if(map.containsKey(digit))  // check if digit can be rotated
28                 {
29                     newNumber = map.get(digit) * m + newNumber;
30                     number /= 10;
31                     m *= 10;
32                 }
33                 else    // if digit is invalid
34                 {
35                     break;
36                 }
37             }
38             
39             if(number == 0 && i != newNumber)
40                 count++;
41                  
42         }
43         
44         return count;
45     }
46 }

参考资料:n/a

LeetCode 题目列表 - LeetCode Questions List

题目来源:https://leetcode.com/

posted @ 2018-05-12 09:26  Jimmy_Cheng  阅读(832)  评论(0编辑  收藏  举报