Standard C++ Library Class Reference

six permutations, which, in order from first to last, are: 1 2 3 , 1 3 2, 2 1 3, 2 3 1, 3 1 2, and 3 2 1.

The prev_permutation algorithm takes a sequence defined by the range [first, last) and

transforms it into its previous permutation, if possible. If such a permutation does exist, the

algorithm completes the transformation and returns true. If the permutation does not exist,

prev_permutation returns false, and transforms the permutation into its "last" permutation

(according to the lexicographical ordering defined by either operator <, the default used in the

first version of the algorithm,or comp, which is user-supplied in the second version of the

algorithm.)

For example, if the sequence defined by [first, last) contains the integers 1 2 3 (in that order),

there is not a "previous permutation." Therefore, the algorithm transforms the sequence into its

last permutation (3 2 1) and returns false.

Complexity

At most (last - first)/2 swaps are performed.

Example

// permute.cpp

#include <numeric> //for accumulate

#include <vector> //for vector

#include <functional> //for less

#include <iostream.h>

int main()

{

//Initialize a vector using an array of ints

int a1[] = {0,0,0,0,1,0,0,0,0,0};

char a2[] = "abcdefghji";

//Create the initial set and copies for permuting

vector<int> m1(a1, a1+10);

vector<int> prev_m1((size_t)10), next_m1((size_t)10);

vector<char> m2(a2, a2+10);

vector<char> prev_m2((size_t)10), next_m2((size_t)10);

copy(m1.begin(), m1.end(), prev_m1.begin());

copy(m1.begin(), m1.end(), next_m1.begin());

copy(m2.begin(), m2.end(), prev_m2.begin());

copy(m2.begin(), m2.end(), next_m2.begin());

//Create permutations

prev_permutation(prev_m1.begin(),

prev_m1.end(),less<int>());

next_permutation(next_m1.begin(),