学步园

//很easy的推理得到一定是1*4=4或者3*2=4之类的。（数字代表数的位数）<br /> #include <assert.h><br /> #include <algorithm><br /> #include <set><br /> #include <iostream></p> <p>unsigned int f(void)<br /> {<br /> typedef std::set<unsigned int> res_set;<br /> res_set res;<br /> unsigned int digits[9];<br /> unsigned int n1, n2, n3, n4, n5;<br /> for( size_t i = 0 ; i < 9 ; ++i ) digits[i] = i + 1;<br /> for( ; ; )<br /> {<br /> n1 = digits[0];<br /> n3 = n1 * 10 + digits[1];<br /> n4 = digits[2] * 100 + digits[3] * 10 + digits[4];<br /> n2 = digits[1] * 1000 + n4;<br /> n5 = digits[5] * 1000 + digits[6] * 100 + digits[7] * 10 + digits[8];<br /> if( (n1 * n2 == n5) || (n3 * n4 == n5) ) res.insert(n5);<br /> if( !std::next_permutation(digits, digits + 9) ) break;<br /> }<br /> unsigned int t = 0;<br /> for( res_set::const_iterator iter = res.begin() ; iter != res.end() ; ++iter ) t += *iter;<br /> return t;<br /> }</p> <p>int main()<br /> {<br /> std::cout << f() << std::endl;<br /> return 0;<br /> }