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std::prev_permutation

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Algorithm Bibliothek
Funktionen
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Functions
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Nicht-modifizierende Sequenz Operationen
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Non-modifying sequence operations
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Modifizierende Sequenz Operationen
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Modifying sequence operations
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Partitionierungsoperationen
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Partitioning operations
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Sortierung Operationen (auf sortierten Bereiche)
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Sorting operations (on sorted ranges)
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Binary Suchaktionen (auf sortierten Bereiche)
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Binary search operations (on sorted ranges)
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Set-Operationen (auf sortierten Bereiche)
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Set operations (on sorted ranges)
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Heap-Operationen
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Heap operations
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Minimum / Maximum Operationen
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Minimum/maximum operations
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Numerische Operationen
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Numeric operations
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C-Bibliothek
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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)
Transformiert den Bereich [first, last) in die vorherige Permutation aus der Menge aller Permutationen, lexikographisch bezüglich operator< oder comp geordnet sind. Versandkosten true wenn solche Permutation existiert, sonst verwandelt den Bereich in den letzten Permutation (wie von std::sort(first, last); std::reverse(first, last);) und kehrt 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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Inhaltsverzeichnis

[Bearbeiten] Parameter

first, last -
das Spektrum der Elemente vertauschen
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.

[Bearbeiten] Rückgabewert

true wenn die neue Permutation geht der alte in lexikographische Ordnung. false wenn die erste Permutation erreicht wurde und der Bereich wurde zurückgesetzt, um die letzte Permutation .
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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[Bearbeiten] Komplexität

An den meisten (last-first)/2 Swaps .
Original:
At most (last-first)/2 swaps.
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[Bearbeiten] Mögliche Implementierung

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;
        }
    }
}

[Bearbeiten] Beispiel

Der folgende Code gibt alle sechs Permutationen der Zeichenfolge "abc" in umgekehrter Reihenfolge
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';
}

Output:

cba cab bca bac acb abc

[Bearbeiten] Siehe auch

determines if a sequence is a permutation of another sequence
(Funktions-Template) [edit]
prev_permutation
generates the next smaller lexicographic permutation of a range of elements
(Funktions-Template) [edit]