hdu 5673 线性求逆元+卡特兰数

gg了gg了，感觉自己一直在刷水题，我noip2017要报零了

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预处理卡特兰数，预处理组合数，然后夹棍法放不走的状态，线性处理逆元

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#include <cstdio>#include <iostream>#include <cstring>using namespace std;const int MAXN = 2000000 + 10;const long long wys = 1000000007; long long cal[MAXN], inv[MAXN], c[MAXN], n;int T;int main() { inv[1] = cal[1] = 1;    for( register long long i = 2; i <= 2000000; i++ ) inv[i] = ( wys - wys / i ) * inv[ wys % i ] % wys;    for( register int i = 2; i <= 2000000; i++ ) {        cal[i] = cal[i - 1] * ( 4 * i -2 ) % wys *inv[ i + 1 ] % wys;     }    scanf( "%d", &T );    while( T-- ){        scanf( "%lld" , &n );        long long ans = 1;        c[0] = 1;        for( register long long i = 1; i <= n; i++ ) c[i] = c[ i - 1 ] * ( n - i + 1 ) % wys * inv[i] % wys;        for( register long long i = 1; ; i++ ) {            int rest = n - ( i << 1 );            if( rest < 0 ) break;            ans = ( ans + cal[i] * c[rest] ) % wys;        }        printf( "%I64d\n", ans);    }    return 0;}