1019 General Palindromic Number (20 分)

1019 Palindromic Number 解析
本文解析了1019 General Palindromic Number问题,介绍了回文数的概念及其在不同进制下的表现。通过给出示例输入输出,详细解释了如何判断一个十进制正整数在特定进制下是否为回文数,并提供了C++代码实现。
1019 General Palindromic Number (20 分)

A number that will be the same when it is written forwards or backwards is known as a Palindromic Number. For example, 1234321 is a palindromic number. All single digit numbers are palindromic numbers.

Although palindromic numbers are most often considered in the decimal system, the concept of palindromicity can be applied to the natural numbers in any numeral system. Consider a number N>0 in base b2, where it is written in standard notation with k+1 digits ai​​ as i=0k​​(ai​​bi​​). Here, as usual, 0ai​​<b for all i and ak​​ is non-zero. Then N is palindromic if and only if ai​​=aki​​ for all i. Zero is written 0 in any base and is also palindromic by definition.

Given any positive decimal integer N and a base b, you are supposed to tell if N is a palindromic number in base b.

Input Specification:

Each input file contains one test case. Each case consists of two positive numbers N and b, where 0<N109​​ is the decimal number and 2b109​​ is the base. The numbers are separated by a space.

Output Specification:

For each test case, first print in one line Yes if N is a palindromic number in base b, or No if not. Then in the next line, print N as the number in base b in the form "ak​​ ak1​​ ... a0​​". Notice that there must be no extra space at the end of output.

Sample Input 1:

27 2

Sample Output 1:

Yes
1 1 0 1 1

Sample Input 2:

121 5

Sample Output 2:

No
4 4 1

水题:进制转换,判断是否回文

 

 1 /**
 2 * Copyright(c)
 3 * All rights reserved.
 4 * Author : Mered1th
 5 * Date : 2019-02-24-01.08.29
 6 * Description : A1019
 7 */
 8 #include<cstdio>
 9 #include<cstring>
10 #include<iostream>
11 #include<cmath>
12 #include<algorithm>
13 #include<string>
14 #include<unordered_set>
15 #include<map>
16 #include<vector>
17 #include<set>
18 using namespace std;
19 const int maxn=1010;
20 bool judge(int s[],int len){
21     for(int i=0;i<len;i++){
22         if(s[i]!=s[len-i-1]){
23             return false;
24         }
25     }
26     return true;
27 }
28 int main(){
29 #ifdef ONLINE_JUDGE
30 #else
31     freopen("1.txt", "r", stdin);
32 #endif
33     int a,n;
34     scanf("%d%d",&a,&n);
35     int num=0,s[maxn]={0};
36     do{
37         s[num++]=a%n;
38         a/=n;
39     }while(a);
40     if(judge(s,num)){
41         printf("Yes\n");
42     }
43     else{
44         printf("No\n");
45     }
46     for(int i=num-1;i>=0;i--){
47         printf("%d",s[i]);
48         if(i>0) printf(" ");
49     }
50     return 0;
51 }

 

转载于:https://www.cnblogs.com/Mered1th/p/10425160.html

### 关于回文子序列的算法及其示例 #### 定义与概念 回文是指正读和反读都相同的字符序列。对于给定字符串中的任意字符组合形成的子序列,如果该子序列满足上述条件,则称为回文子序列。 #### 动态规划求解最长回文子序列 为了找到一个字符串中最长的回文子序列,可以采用动态规划的方法来解决这个问题。设 `dp[i][j]` 表示从第 i 到 j 的子串内的最长回文子序列长度: - 当 s[i]==s[j] 时, dp[i][j]=dp[i+1][j−1]+2; - 否则, dp[i][j]=max(dp[i+1][j],dp[i][j−1]). 最终的结果保存在 `dp[0][len(s)-1]` 中[^3]. ```python def longest_palindromic_subseq(s: str) -> int: n = len(s) # 创建二维数组用于存储中间结果 dp = [[0]*n for _ in range(n)] # 初始化单个字符的情况 for i in range(n): dp[i][i] = 1 # 填充表格 for length in range(2, n + 1): for start in range(n - length + 1): end = start + length - 1 if s[start] == s[end]: dp[start][end] = dp[start+1][end-1] + 2 else: dp[start][end] = max(dp[start+1][end], dp[start][end-1]) return dp[0][-1] ``` 此方法的时间复杂度为 O(),空间复杂度同样为 O(). #### 枚举所有可能的回文子序列 除了寻找最长的回文子序列外,还可以通过枚举的方式找出所有的不同回文子序列。这种方法适用于较短的输入字符串,并且可以通过位掩码技术实现高效的遍历。 ```python from collections import defaultdict def count_distinct_palindrome_subsequences(text: str) -> list[str]: results = set() memo = {} def backtrack(start=0, path=""): nonlocal text, results, memo key = (start, path) if key not in memo: temp_set = {path} if path == path[::-1] else {} for index in range(start, len(text)): new_path = path + text[index] if new_path == new_path[::-1]: temp_set.add(new_path) temp_set |= backtrack(index + 1, new_path) memo[key] = temp_set results.update(memo[(start, path)]) return memo[(start, path)] backtrack() return sorted(list(results)) ``` 这段代码会返回按字典序排列的不同回文子序列列表.
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