# Power Set in Lexicographic order

Examples :

```Input : abc
Output : a ab abc ac b bc c
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

The idea is to sort array first. After sorting, one by one fix characters and recursively generates all subsets starting from them. After every recursive call, we remove last character so that next permutation can be generated.

## C++

 `// CPP program to generate power set in ` `// lexicographic order. ` `#include ` `using` `namespace` `std; ` ` `  `// str : Stores input string ` `// n : Length of str. ` `// curr : Stores current permutation ` `// index : Index in current permutation, curr ` `void` `permuteRec(string str, ``int` `n, ` `           ``int` `index = -1, string curr = ``""``) ` `{ ` `    ``// base case ` `    ``if` `(index == n)  ` `        ``return``; ` ` `  `    ``cout << curr << ````" "````; ` `    ``for` `(``int` `i = index + 1; i < n; i++) { ` ` `  `        ``curr += str[i]; ` `        ``permuteRec(str, n, i, curr); ` `  `  `        ``// backtracking ` `        ``curr = curr.erase(curr.size() - 1);  ` `    ``} ` `    ``return``; ` `} ` ` `  `// Generates power set in lexicographic ` `// order. ` `void` `powerSet(string str) ` `{ ` `    ``sort(str.begin(), str.end()); ` `    ``permuteRec(str, str.size()); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"cab"``; ` `    ``powerSet(str); ` `    ``return` `0; ` `} `

## 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

## PHP

 ` `

Output :

```a
ab
abc
ac
b
bc
c
```