给定一个字符串str，打印字典顺序字符串的所有组合。
例子：
Input: str = "ABC"
Output:
A
AB
ABC
AC
ACB
B
BA
BAC
BC
BCA
C
CA
CAB
CB
CBA
Input: ED
Output:
D
DE
E
ED
方法：使用映射计数字符串中所有字符的出现，然后使用递归可以打印所有可能的组合。将元素及其数量存储在两个不同的数组中。三个阵列被使用，其具有字符输入[]数组，计数[]阵列具有字符和结果[]是被在递归用于产生所有组合一个临时数组的计数。使用递归和回溯，可以打印所有组合。
下面是上述方法的实现。
C++
// C++ program to find all combinations
// of a string in lexicographical order
#include
using namespace std;
// function to print string
void printResult(char* result, int len)
{
for (int i = 0; i <= len; i++)
cout << result[i];
cout << endl;
}
// Method to found all combination
// of string it is based in tree
void stringCombination(char result[], char str[], int count[],
int level, int size, int length)
{
// return if level is equal size of string
if (level == size)
return;
for (int i = 0; i < length; i++) {
// if occurrence of char is 0 then
// skip the iteration of loop
if (count[i] == 0)
continue;
// decrease the char occurrence by 1
count[i]--;
// store the char in result
result[level] = str[i];
// print the string till level
printResult(result, level);
// call the function from level +1
stringCombination(result, str, count,
level + 1, size, length);
// backtracking
count[i]++;
}
}
void combination(string str)
{
// declare the map for store
// each char with occurrence
map mp;
for (int i = 0; i < str.size(); i++) {
if (mp.find(str[i]) != mp.end())
mp[str[i]] = mp[str[i]] + 1;
else
mp[str[i]] = 1;
}
// initialize the input array
// with all unique char
char* input = new char[mp.size()];
// initialize the count array with
// occurrence the unique char
int* count = new int[mp.size()];
// temporary char array for store the result
char* result = new char[str.size()];
map::iterator it = mp.begin();
int i = 0;
for (it; it != mp.end(); it++) {
// store the element of input array
input[i] = it->first;
// store the element of count array
count[i] = it->second;
i++;
}
// size of map(no of unique char)
int length = mp.size();
// size of original string
int size = str.size();
// call function for print string combination
stringCombination(result, input, count,
0, size, length);
}
// Driver code
int main()
{
string str = "ABC";
combination(str);
return 0;
} Java
// Java program to find all combinations
// of a string in lexicographical order
import java.util.HashMap;
class GFG
{
// function to print string
static void printResult(char[] result,
int len)
{
for (int i = 0; i <= len; i++)
System.out.print(result[i]);
System.out.println();
}
// Method to found all combination
// of string it is based in tree
static void stringCombination(char[] result, char[] str,
int[] count, int level,
int size, int length)
{
// return if level is equal size of string
if (level == size)
return;
for (int i = 0; i < length; i++)
{
// if occurrence of char is 0 then
// skip the iteration of loop
if (count[i] == 0)
continue;
// decrease the char occurrence by 1
count[i]--;
// store the char in result
result[level] = str[i];
// print the string till level
printResult(result, level);
// call the function from level +1
stringCombination(result, str, count,
level + 1, size, length);
// backtracking
count[i]++;
}
}
static void combination(String str)
{
// declare the map for store
// each char with occurrence
HashMap mp = new HashMap<>();
for (int i = 0; i < str.length(); i++)
mp.put(str.charAt(i), mp.get(str.charAt(i)) == null ? 1 :
mp.get(str.charAt(i)) + 1);
// initialize the input array
// with all unique char
char[] input = new char[mp.size()];
// initialize the count array with
// occurrence the unique char
int[] count = new int[mp.size()];
// temporary char array for store the result
char[] result = new char[str.length()];
int i = 0;
for (HashMap.Entry entry : mp.entrySet())
{
// store the element of input array
input[i] = entry.getKey();
// store the element of count array
count[i] = entry.getValue();
i++;
}
// size of map(no of unique char)
int length = mp.size();
// size of original string
int size = str.length();
// call function for print string combination
stringCombination(result, input, count, 0,
size, length);
}
// Driver code
public static void main (String[] args)
{
String str = "ABC";
combination(str);
}
}
// This code is contributed by
// sanjeev2552 C#
// C# program to find all combinations
// of a string in lexicographical order
using System;
using System.Collections.Generic;
class GFG
{
// function to print string
static void printResult(char[] result,
int len)
{
for (int i = 0; i <= len; i++)
Console.Write(result[i]);
Console.WriteLine();
}
// Method to found all combination
// of string it is based in tree
static void stringCombination(char[] result, char[] str,
int[] count, int level,
int size, int length)
{
// return if level is equal size of string
if (level == size)
return;
for (int i = 0; i < length; i++)
{
// if occurrence of char is 0 then
// skip the iteration of loop
if (count[i] == 0)
continue;
// decrease the char occurrence by 1
count[i]--;
// store the char in result
result[level] = str[i];
// print the string till level
printResult(result, level);
// call the function from level +1
stringCombination(result, str, count,
level + 1, size, length);
// backtracking
count[i]++;
}
}
static void combination(String str)
{
int i;
// declare the map for store
// each char with occurrence
Dictionary mp = new Dictionary();
for (i= 0; i < str.Length; i++)
if(mp.ContainsKey(str[i]))
mp[str[i]] = mp[str[i]] + 1;
else
mp.Add(str[i], 1);
// initialize the input array
// with all unique char
char[] input = new char[mp.Count];
// initialize the count array with
// occurrence the unique char
int[] count = new int[mp.Count];
// temporary char array for store the result
char[] result = new char[str.Length];
i = 0;
foreach(KeyValuePair entry in mp)
{
// store the element of input array
input[i] = entry.Key;
// store the element of count array
count[i] = entry.Value;
i++;
}
// size of map(no of unique char)
int length = mp.Count;
// size of original string
int size = str.Length;
// call function for print string combination
stringCombination(result, input, count, 0,
size, length);
}
// Driver code
public static void Main(String[] args)
{
String str = "ABC";
combination(str);
}
}
// This code is contributed by Rajput-Ji 输出：
A
AB
ABC
AC
ACB
B
BA
BAC
BC
BCA
C
CA
CAB
CB
CBA