TOJ--1507--大数乘法的初步实现

 1 // 寻找7 
 2 #include <iostream>
 3 #include <cstring>
 4 using namespace std;
 5 
 6 int k , m;
 7 const int size = 1010;
 8 int ch[3];
 9 int temp[size];
10 int str[size];
11 
12 void multiply()
13 {
14     int len , t , x;
15     memset( temp , 0 , sizeof(temp) );
16     if(m<10)
17     {
18         ch[0] = m;
19         ch[1] = ch[2] = 0;
20         x = 1;
21     }
22     else if(m>=10&&m<100)
23     {
24         ch[0] = m/10;
25         ch[1] = m%10;
26         ch[2] = 0;
27         x = 2;
28     }
29     else
30     {
31         ch[0] = m/100;
32         ch[1] = (m%100)/10;
33         ch[2] = (m%100)%10; 
34         x = 3;
35     }
36     temp[0] = 1;
37     len = 1;
38     for( int n = 1 ; ; n++ )
39     {
40         memset( str , 0 , sizeof(str) );
41         for( int i = 0 ; i<x ; i++ )
42         {
43             for( int j = 0 ; j<len ; j++ )
44             {
45                 str[i+j+1]+=ch[i]*temp[j];
46             }
47         }
48         for( int i = x+len-1 ; i>=1 ; i-- )
49         {
50             if( str[i]>=10 )
51             {
52                 str[i-1]+=str[i]/10;
53                 str[i]%=10;
54             }
55         }
56         if( str[0]!=0 )
57             t = 0;
58         else
59             t = 1;
60         int tt = t;
61         for( int j = 0 ; t<x+len ; t++ , j++ )
62         {
63             temp[j] = str[t];
64         }
65         if( str[x+len-k]==7 )
66         {
67             cout<<n<<endl;
68             break;
69         }
70         len+=x-tt;
71     }
72 }
73 
74 int main()
75 {
76     while(cin>>k>>m)
77     {
78         multiply();
79     }    
80     return 0;
81 }