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字母重组算法

最新推荐文章于 2020-03-10 23:05:30 发布

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本文介绍了一种使用回溯法实现字母重组的算法，该算法能够从给定的一组字母中生成所有可能的不同排列，并确保输出结果的字典序。文中提供了详细的代码实现，包括通过比较函数处理大小写字母的方法。

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Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 12070		Accepted: 4933

Description

You are to write a program that has to generate all possible words from a given set of letters.
Example: Given the word "abc", your program should - by exploring all different combination of the three letters - output the words "abc", "acb", "bac", "bca", "cab" and "cba".
In the word taken from the input file, some letters may appear more than once. For a given word, your program should not produce the same word more than once, and the words should be output in alphabetically ascending order.

Input

The input consists of several words. The first line contains a number giving the number of words to follow. Each following line contains one word. A word consists of uppercase or lowercase letters from A to Z. Uppercase and lowercase letters are to be considered different. The length of each word is less than 13.

Output

For each word in the input, the output should contain all different words that can be generated with the letters of the given word. The words generated from the same input word should be output in alphabetically ascending order. An upper case letter goes before the corresponding lower case letter.

Sample Input

3
aAb
abc
acba

Sample Output

Aab
Aba
aAb
abA
bAa
baA
abc
acb
bac
bca
cab
cba
aabc
aacb
abac
abca
acab
acba
baac
baca
bcaa
caab
caba
cbaa

Hint

An upper case letter goes before the corresponding lower case letter.
So the right order of letters is 'A'<'a'<'B'<'b'<...<'Z'<'z'.

Source

回溯法

#include<stdio.h>

#include<algorithm>

#include<cctype>

using namespace std;

char s[20];

char res[20];

bool b[20];

int N;

int cmp(char a,char b)

{

if(islower(a)&&islower(b)) return a<b;

if(isupper(a)&&isupper(b)) return a<b;

if(islower(a)&&isupper(b)) return a<(b-'A'+'a');

if(isupper(a)&&islower(b)) return a<=(b-'a'+'A');

}

void backtrace(int n)

{

if(n==N)

{

printf("%s/n",res);

return ;

}

int i;

for(i=0; i<N; ++i)

{

if(b[i]==false)

{

res[n]=s[i];

b[i]=true;

backtrace(n+1);

b[i]=false;

while(i<(N-1) && s[i]==s[i+1])//跳过相同的字符

i++;

}

int main()

{

int T;

while(scanf("%d",&T)!=EOF)

{

while(T--)

{

scanf("%s",&s);

N=strlen(s);

res[N]='/0';

sort(s,s+N,cmp);

memset(b,0,sizeof(b));

backtrace(0);

}

return 0;

}

STL:

#include<cstdio>

#include<cstring>

#include<cctype>

#include<algorithm>

using namespace std;

char str[20];

bool cmp(char a,char b)

{

/*if(islower(a)&&islower(b)) return a<b;

if(isupper(a)&&isupper(b)) return a<b;

if(islower(a)&&isupper(b)) return a<(b-'A'+'a');

if(isupper(a)&&islower(b)) return a<=(b-'a'+'A');*/

if(tolower(a)==tolower(b)) return a<b;

return tolower(a)<tolower(b);

}

int main()

{

int T;

while(scanf("%d",&T)!=EOF)

{

while(T--)

{

scanf("%s",str);

int n=strlen(str);

sort(str,str+n,cmp);

printf("%s/n",str);

while(next_permutation(str,str+n,cmp))//别忘了加CMP

printf("%s/n",str);

}

return 0;

}