算法 全排列的应用

 
#include <iostream>
#include <string>using namespace std;// 交换字符串中两个字符的位置
void swap(char& a, char& b)
{char temp = a;a = b;b = temp;
}void fun(string str) {string a = str.substr(0,4);    int aa;sscanf(a.c_str(), "%d", &aa);string b = str.substr(4,1);int bb;sscanf(b.c_str(), "%d", &bb);string c = str.substr(5, 4);int cc;sscanf(c.c_str(), "%d", &cc);if (aa == bb * cc) {cout << aa << " = " << bb << " x " << cc << endl;}b = str.substr(4, 2);    sscanf(b.c_str(), "%d", &bb);c = str.substr(6, 3);    sscanf(c.c_str(), "%d", &cc);if (aa == bb * cc) {cout << aa << " = " << bb << " x " << cc << endl;}}// 字符串全排列函数
void permutation(string str, int begin, int end)
{if (begin == end) // 当begin等于end时，表示已经得到一个排列{fun(str); // 输出该排列}else{for (int i = begin; i <= end; i++){// 将第i个字符与第begin个字符交换位置swap(str[begin], str[i]);// 对begin+1到end的子串进行全排列permutation(str, begin + 1, end);// 将第i个字符与第begin个字符交换位置，恢复原来的顺序swap(str[begin], str[i]);}}
}int main()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
{string str = "123456789";permutation(str, 0, str.size() - 1);}