本文是关于按字典顺序生成幂集的。
例子 :
Input : abc
Output : a ab abc ac b bc c
这个想法是先对数组排序。排序后,一个一个固定的字符并递归地从它们开始生成所有子集。在每个递归调用之后,我们都删除最后一个字符,以便可以生成下一个排列。
C++
// CPP program to generate power set in
// lexicographic order.
#include
using namespace std;
// str : Stores input string
// n : Length of str.
void func(string s, vector& str, int n, int pow_set)
{
int i, j;
for (i = 0; i < pow_set; i++) {
string x;
for (j = 0; j < n; j++) {
if (i & 1 << j) {
x = x + s[j];
}
}
if (i != 0)
str.push_back(x);
}
}
int main()
{
int n;
string s;
vector str;
s = "cab";
n = s.length();
int pow_set = pow(2, n);
func(s, str, n, pow_set);
sort(str.begin(), str.end());
for (int i = 0; i < str.size(); i++)
cout << str[i] << " ";
cout << endl;
return 0;
}
Java
// Java program to generate power set in
// lexicographic order.
import java.util.*;
class GFG {
// str : Stores input string
// n : Length of str.
// curr : Stores current permutation
// index : Index in current permutation, curr
static void permuteRec(String str, int n,
int index, String curr)
{
// base case
if (index == n) {
return;
}
System.out.println(curr);
for (int i = index + 1; i < n; i++) {
curr += str.charAt(i);
permuteRec(str, n, i, curr);
// backtracking
curr = curr.substring(0, curr.length() - 1);
}
return;
}
// Generates power set in lexicographic
// order.
static void powerSet(String str)
{
char[] arr = str.toCharArray();
Arrays.sort(arr);
permuteRec(new String(arr), str.length(), -1, "");
}
// Driver code
public static void main(String[] args)
{
String str = "cab";
powerSet(str);
}
}
/* This code contributed by PrinciRaj1992 */
Python3
# Python3 program to generate power
# set in lexicographic order.
# str : Stores input string
# n : Length of str.
# curr : Stores current permutation
# index : Index in current permutation, curr
def permuteRec(string, n, index = -1, curr = ""):
# base case
if index == n:
return
if len(curr) > 0:
print(curr)
for i in range(index + 1, n):
curr += string[i]
permuteRec(string, n, i, curr)
# backtracking
curr = curr[:len(curr) - 1]
# Generates power set in lexicographic order
def powerSet(string):
string = ''.join(sorted(string))
permuteRec(string, len(string))
# Driver Code
if __name__ == "__main__":
string = "cab"
powerSet(string)
# This code is contributed by vibhu4agarwal
C#
// C# program to generate power set in
// lexicographic order.
using System;
class GFG {
// str : Stores input string
// n : Length of str.
// curr : Stores current permutation
// index : Index in current permutation, curr
static void permuteRec(String str, int n,
int index, String curr)
{
// base case
if (index == n) {
return;
}
Console.WriteLine(curr);
for (int i = index + 1; i < n; i++) {
curr += str[i];
permuteRec(str, n, i, curr);
// backtracking
curr = curr.Substring(0, curr.Length - 1);
}
return;
}
// Generates power set in lexicographic
// order.
static void powerSet(String str)
{
char[] arr = str.ToCharArray();
Array.Sort(arr);
permuteRec(new String(arr), str.Length, -1, "");
}
// Driver code
public static void Main(String[] args)
{
String str = "cab";
powerSet(str);
}
}
// This code contributed by Rajput-Ji
PHP
输出
a ab b c ca cab cb