1 //字符串的乘法
2 string multi(string a, string b){
3 int i, j, arr[200], len = a.length() + b.length();
4 memset(arr, 0, sizeof arr);
5 reverse(a.begin(), a.end());
6 reverse(b.begin(), b.end());
7 for (int i = 0; i<a.length(); i++)
8 for (int j = 0; j<b.length(); j++)
9 arr[i + j] += (a[i] - '0')*(b[j] - '0');
10 for (int i = 0; i<len; i++){
11 arr[i + 1] += arr[i] / 10;
12 arr[i] %= 10;
13 }
14 string ret = string(len, '0');
15 for (int i = 0; i<len; i++)
16 ret[i] += arr[i];
17 reverse(ret.begin(), ret.end());//翻转
18 return ret;
19 }
20
21 //x ^ n
22 string Str_Pow(string x, int p){
23 string ret = "1";
24 while (p){
25 if (p & 1) ret = multi(ret, x);
26 x = multi(x, x);
27 p >>= 1;
28 }
29 return ret;
30 }
