#include using namespace std; #define pi acos(-1) #define N 1000000007 #define ll long long #define ull unsigned long long #define mem(a) memset(a,0,sizeof(a)) int main() { string s; //截取字串: s.substr(pos,n); //截取s中从pos开始(包括0)的n个字符的字串 s.substr(pos); //截取s中从pos开
