面试题 06162012 [1]

/*Permutations of a string are defined to be all possible orderings of the characters within the string. For example, the string "cat" has the following permutations:{ "cat", "cta","atc","act","tca","tac" }Write an efficient C/C++ function, generate_permutations(), that will generate all the permutations of a given string. This program is expected to be invoked with the input string as the only parameter and expected to output the results to the standard output.Assumption : If the characters in the string are duplicated, some permutations will be identical, however they are still listed out. For example, "all" will generate the following permutations: { "all","all","lal","lal","lla","lla" }Function prototype : void generate_permutations(const char* input_string)Test run : void generate_permutations("eyjafjallajokull").*/#include <iostream>#include <hash_set>#include <string>std::hash_set<std::string> strSet;void swap(char* x, char* y){char temp;temp = *x;*x = *y;*y = temp;};void permute(char* a, int i, int n){if(i == n){std::string curWord(a);if(strSet.find(curWord) == strSet.end()){strSet.insert(a);printf("%s\n", a);}}else{for(int j = i; j <= n; j++){swap(a + i, a + j);permute(a, i + 1, n);swap(a + i, a + j);}}};int main(){char a[] = "caat";permute(a, 0, 3);return 0;}