std::next_permutation and prev_permutation in C++

In C++, next_permutation() and prev_permutation() (in <algorithm>) rearrange a container’s elements into the next or previous lexicographical order among all possible permutations.

std::next_permutation()

The std::next_permutation in C++ is used to rearrange the elements of the given range [first, last) to the lexicographical larger permutation if it exists.

Syntax

std::next_permutation(first, last);

Parameters

• first: Iterator to the first element of the given range.
• last: Iterator to the theoretical element just after the last element of the given range.

Return Value

• Returns true if the container could be rearranged to the to the lexicographical larger permutation.
• Returns false otherwise.

1 2 3 
1 3 2 
2 1 3 
2 3 1 
3 1 2 
3 2 1 

Explanation: The total number of permutations of vector of 3 elements is 3! = 6. We already took the smallest possible permutation as the starting point, so we were able to print all the permutations using next_permutation().

std::prev_permutation()

The std::prev_permutation is used to rearrange the elements of the given range [first, last) in the lexicographical smaller permutation if it exists.

Syntax

std::prev_permutataion(first, last)

Parameters

• first: Iterator to the first element of the given range.
• last: Iterator to the theoretical element just after the last element of the given range.

Return Value

• Returns true if the container could be rearranged to the to the lexicographical smaller permutation.
• Returns false otherwise.

2 1 3 
1 3 2 
1 2 3 

Explanation: The total number of permutations of vector of 3 elements is 3! = 6. But we were only able to print 3 permutations because we didn't took the largest permutation as starting point for prev_permutation() function. So, all the permutation greater than the permutation {2, 1, 3} are left out.