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std::prev_permutation

Da cppreference.com.
< cpp‎ | algorithm

 
 
Algoritmo libreria
Funzioni
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Functions
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Non modifica le operazioni di sequenza
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Non-modifying sequence operations
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Modifica delle operazioni di sequenza
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Modifying sequence operations
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Partizionamento operazioni
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Partitioning operations
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Ordinamento delle operazioni (su intervalli ordinati)
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Sorting operations (on sorted ranges)
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Binarie (le operazioni di ricerca sui campi ordinati)
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Binary search operations (on sorted ranges)
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Impostare le operazioni (su intervalli ordinati)
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Set operations (on sorted ranges)
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Heap operazioni
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Heap operations
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Minimo / massimo le operazioni
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Minimum/maximum operations
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Operazioni numeriche
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Numeric operations
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Libreria 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)
Trasforma il [first, last) gamma nella permutazione precedente da l'insieme di tutte le permutazioni che sono classificati in ordine lessicografico rispetto al operator< o comp. true Restituisce se esiste permutazione, trasforma altrimenti il ​​campo nella permutazione ultimo (come per std::sort(first, last); std::reverse(first, last);) e ritorna 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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Indice

[modifica] Parametri

first, last -
la gamma di elementi per permutare
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.

[modifica] Valore di ritorno

true se la permutazione nuovo precede il vecchio in ordine lessicografico. false se la permutazione primo è stato raggiunto e la gamma è stato reimpostato per la permutazione all'ultimo.
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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[modifica] Complessità

Alla maggior parte delle operazioni di swap (last-first)/2.
Original:
At most (last-first)/2 swaps.
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[modifica] Possibile implementazione

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;
        }
    }
}

[modifica] Esempio

Il codice seguente consente di stampare tutte le sei permutazioni della stringa "abc" in ordine inverso
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

[modifica] Vedi anche

determines if a sequence is a permutation of another sequence
(funzione di modello) [edit]
prev_permutation
generates the next smaller lexicographic permutation of a range of elements
(funzione di modello) [edit]