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Permutations in C++
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| /* | |
| * Print all permutations of string ``s´´. | |
| */ | |
| #include <stdio.h> | |
| static const char s[] = "abc"; | |
| const int MAX = (sizeof(s)/sizeof(char)) - 1; | |
| void print(int counts[MAX]) | |
| { | |
| for ( int n=0; n<MAX; ++n ) | |
| printf("%c", s[counts[n]]); | |
| printf("\n"); | |
| } | |
| void inc(int counts[MAX], int p = 0) | |
| { | |
| if ( p < MAX && ++counts[p] >= MAX ) { | |
| counts[p] = 0; | |
| inc(counts, p+1); | |
| } | |
| } | |
| bool zero(int counts[MAX]) | |
| { | |
| for ( int p=0; p < MAX; ++p ) | |
| if ( counts[p] != 0 ) | |
| return false; | |
| return true; | |
| } | |
| bool uniq(int counts[MAX]) | |
| { | |
| for ( int p=0; p<MAX; ++p ) | |
| for ( int i=p+1; i<MAX; ++i ) | |
| if ( counts[p] == counts[i] ) | |
| return false; | |
| return true; | |
| } | |
| int main() | |
| { | |
| int counts[MAX] = {0, 0, 0}; | |
| do { | |
| if ( uniq(counts) ) print(counts); | |
| inc(counts); | |
| } while ( !zero(counts) ); | |
| } |
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Made uniq run in O(n) instead of O(n^2).