void permute(char *a,int i,int n) {
if (i == (n-1)) printf("\"%s\"\n",a);
else {
for (int j = i; j < n; j++) {
swap((a+i),(a+j));
permute(a,i+1,n);
swap((a+i),(a+j));
}
}
}
我有例如字符串abc,所以我想按照左列列出的字典顺序接收所有排列,但是我的结果如右栏所示.
"abc" "abc"
"acb" "acb"
"bac" "bac"
"bca" "bca"
"cab" <
"cba" "cba"
> "cab"
有人可以帮我弄这个吗？我看到一些算法,但他们看起来很困难.我想我可以将所有生成的字符串保存在数组中,然后对该数组进行排序,但是我无法写入(我是初学者C).
解决方法
在geeksforgeeks上有一个非常简单的算法描述(加上实现)：
Given a string,print all permutations of it in sorted order. For
example,if the input string is “ABC”,then output should be “ABC,
ACB,BAC,BCA,CAB,CBA”.We have discussed a program to print all permutations in this post,
but here we must print the permutations in increasing order.Following are the steps to print the permutations lexicographic-ally
Sort the given string in non-decreasing order and print it. The first permutation is always the string sorted in non-decreasing order.
Start generating next higher permutation. Do it until next higher permutation is not possible. If we reach a permutation where all
characters are sorted in non-increasing order,then that permutation
is the last permutation.Steps to generate the next higher permutation:
1. Take the prevIoUsly printed permutation and find the rightmost character in it,which is smaller than its next character. Let us call
this character as ‘first character’.
Now find the ceiling of the ‘first character’. Ceiling is the smallest character on right of ‘first character’,which is greater
than ‘first character’. Let us call the ceil character as ‘second
character’.Swap the two characters found in above 2 steps.
Sort the substring (in non-decreasing order) after the original index of ‘first character’.
我在下面重新实现了：
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void swap(char* left,char* right)
{
char temp = *left;
*left = *right;
*right = temp;
}
int compare (const void * a,const void * b)
{
return ( *(char*)a - *(char*)b );
}
void PrintSortedPermutations(char* inStr)
{
// Re-implementation of algorithm described here:
// http://www.geeksforgeeks.org/lexicographic-permutations-of-string/
int strSize = strlen(inStr);
// 0. Ensure input container is sorted
qsort(inStr,strSize,sizeof(char),compare);
int largerPermFound = 1;
do{
// 1. Print next permutation
printf("%s\n",inStr);
// 2. Find rightmost char that is smaller than char to its right
int i;
for (i = strSize - 2; i >= 0 && inStr[i] >= inStr[i+1]; --i){}
// if we Couldn't find one,we're finished,else we can swap somewhere
if (i > -1)
{
// 3 find character at index j such that
// inStr[j] = min(inStr[k]) && inStr[k] > inStr[i] for all k > i
int j = i+1;
int k;
for(k=j;k<strSize && inStr[k];++k)
{
if (inStr[k] > inStr[i] && inStr[k] < inStr[j])
j = k;
}
// 3. Swap chars at i and j
swap(&inStr[i],&inStr[j]);
// 4. Sort string to the right of i
qsort(inStr+i+1,strSize-i-1,compare);
}
else
{
largerPermFound = 0;
}
}while(largerPermFound);
}
int main(void) {
char str[] = "abc";
PrintSortedPermutations(str);
return 0;
}
产量
abc
acb
bac
bca
cab
cba
Live Demo
在C
std::next_permutation从< algorithm>图书馆将为您做这件事,只需确保您先对容器进行排序：
Return value
true if the function Could rearrange the object as a lexicographicaly
greater permutation. Otherwise,the function returns false to indicate
that the arrangement is not greater than the prevIoUs,but the lowest
possible (sorted in ascending order).
例如：
std::string myStr = "abc";
std::stable_sort(std::begin(myStr),std::end(myStr));
do {
for(auto&& element : myStr)
std::cout << element << " ";
std::cout << std::endl;
} while (std::next_permutation(std::begin(myStr),std::end(myStr)));
输出：
a b c
a c b
b a c
b c a
c a b
c b a
Live Demo