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//设n的逆元为k，x/n%moder == x%moder*k%moder%moder//运用等比数列求和公式 #include<iostream>using namespace std;typedef long long ll;const ll P=1e9+7;void open_file(){ freopen("sum.in","r",stdin); freopen

http://www.cnblogs.com/candy99/p/6073906.html