按词典顺序排列的功率集

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

输出

a ab b c ca cab cb