"STL Source Code Analysis"--next_permutation function

The STL provides 2 algorithms for calculating permutations and combinations of relationships. Next_permucation and Prev_permutaion, respectively.

Next_permutation is used to calculate the composition of the next dictionary order, and Prev_permutation is used to calculate the permutation of the previous (prev) dictionary order.

Dictionary sorting refers to the arrangement of permutations, sorted by size from small to large, such as the 123 arrangement, and the dictionary sort to 123,132,213,231,312,321.

Take a look at the implementation principle of next_permutation:
Looking forward from the back of the sequence, found two adjacent elements P[n] and p[n+1], and P[n]

Template < class _bidirectionaliter>bool next_permutation(_bidirectionaliter  __first, _bidirectionaliter __last) {__stl_requires (_bidirectionaliter, _bidirectionaliterator); __stl_requires (TypeName Iterator_traits<_bidirectionaliter>::value_type, _lessthancomparable);if(__first = = __last)//Empty collection    return false;  _bidirectionaliter __i = __first; ++__i;if(__i = = __last)//Only one element    return false;  __i = __last; --__i;//Last element   for(;;)    {_bidirectionaliter __ii = __i; --__i;if(*__i < *__ii) {//Find p[n]<p[n+1]_bidirectionaliter __j = __last; while(! (*__i < *--__j))//Find P[m]{} iter_swap (__i, __j);Reverse(__ii, __last);//Reverse sort      return true; }if(__i = = __first) {//arrive at the front not to find meet p[n]<p[n+1], lined up      Reverse(__first, __last);return false; }  }}

For custom types, the comparison size can be passed into the function pointer, and the prototype is:

first,                         last, Compare comp);

Test:

#include <iostream>#include <vector>#include <algorithm>voidPrint (STD:: vector<int>& V) { for(STD:: vector<int>:: Iterator It=v.begin (); It!=v.end (); ++it) {STD::cout<<*it<<" "; }STD::cout<<STD:: Endl;}intMain () {STD:: vector<int>V V.reserve (5); for(intI=1; i<=5;    ++i) {v.push_back (i); } Do{Print (V); } while(STD:: Next_permutation (V.begin (), V.end ()));return 0;}

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"STL Source Code Analysis"--next_permutation function