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std::prev_permutation

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< cpp‎ | algorithm

 
 
Bibliothèque d'algorithmes
Fonctions
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Functions
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Non-modification de la séquence des opérations
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Non-modifying sequence operations
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Modification de la séquence des opérations
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Modifying sequence operations
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Des opérations de partitionnement
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Partitioning operations
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Opérations de tri (sur les gammes triés)
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Sorting operations (on sorted ranges)
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is_sorted (C++11)
is_sorted_until (C++11)
sort
Opérations binaires de recherche (sur les gammes triés)
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Binary search operations (on sorted ranges)
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Définir les opérations (sur les gammes triés)
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Set operations (on sorted ranges)
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Opérations Heap
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Heap operations
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Minimum / maximum de fonctionnement
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Minimum/maximum operations
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Opérations numériques
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Numeric operations
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Bibliothèque C
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C library
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Defined in header <algorithm>
template< class BidirIt >
bool prev_permutation( BidirIt first, BidirIt last);
(1)
template< class BidirIt, class Compare >
bool prev_permutation( BidirIt first, BidirIt last, Compare comp);
(2)
Transforme la gamme [first, last) dans la permutation précédente de l'ensemble de toutes les permutations qui sont lexicographiquement ordonnées par rapport à operator< ou comp. true Retours s'il en existe permutation, autrement transforme la plage dans la dernière permutation (comme par std::sort(first, last); std::reverse(first, last);) et retourne false .
Original:
Transforms the range [first, last) into the previous permutation from the set of all permutations that are lexicographically ordered with respect to operator< or comp. Returns true if such permutation exists, otherwise transforms the range into the last permutation (as if by std::sort(first, last); std::reverse(first, last);) and returns false.
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Sommaire

[modifier] Paramètres

first, last -
la plage d'éléments à permuter
Original:
the range of elements to permute
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comp - comparison function which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type BidirIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
BidirIt must meet the requirements of ValueSwappable and BidirectionalIterator.

[modifier] Retourne la valeur

true si la nouvelle permutation précède l'ancien dans l'ordre lexicographique. false si la première permutation a été atteint et la gamme a été remis à la permutation dernière .
Original:
true if the new permutation precedes the old in lexicographical order. false if the first permutation was reached and the range was reset to the last permutation.
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[modifier] Complexité

À la plupart des swaps (last-first)/2 .
Original:
At most (last-first)/2 swaps.
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[modifier] Mise en œuvre possible

template<class BidirIt>
bool prev_permutation(BidirIt first, BidirIt last)
{
    if (first == last) return false;
    BidirIt i = last;
    if (first == --i) return false;
 
    while (1) {
        BidirIt i1, i2;
 
        i1 = i;
        if (*i1 < *--i) {
            i2 = last;
            while (!(*--i2 < *i))
                ;
            std::iter_swap(i, i2);
            std::reverse(i1, last);
            return true;
        }
        if (i == first) {
            std::reverse(first, last);
            return false;
        }
    }
}

[modifier] Exemple

Le code suivant imprime tous les six permutations de la chaîne "abc" dans l'ordre inverse
Original:
The following code prints all six permutations of the string "abc" in reverse order
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#include <algorithm>
#include <string>
#include <iostream>
#include <functional>
int main()
{
    std::string s="abc";
    std::sort(s.begin(), s.end(), std::greater<char>());
    do {
        std::cout << s << ' ';
    } while(std::prev_permutation(s.begin(), s.end()));
    std::cout << '\n';
}

Résultat :

cba cab bca bac acb abc

[modifier] Voir aussi

determines if a sequence is a permutation of another sequence
(fonction générique) [edit]
prev_permutation
lexicographique génère le plus petit côté d'une permutation série d'éléments
Original:
generates the next smaller lexicographic permutation of a range of elements
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(fonction générique) [edit]