2017"百度之星"程序设计大赛 - 资格赛 寻找母串

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 //计算n的k次方对M取模，二分法
 5 ll Pow(ll n, ll k, ll p){
 6     ll ans=1;
 7     while(k){
 8         if(k&1)
 9             ans=(ans*n)%p;
10         n = (n*n)%p;
11         k>>=1; //k=k>>1  k=k/2；
12     }
13     return ans;
14 }
15 ll C(ll n,ll m,ll p){
16     if(m==0) return 1;
17     if(m>n-m) m=n-m;
18     ll up=1,down=1;
19     for(int i=1;i<=m;i++){
20         up = (up*(n-i+1))%p;
21         down=(down*i)%p;
22     }
23     return up*Pow(down,p-2,p)%p;
24 }
25 ll lucas(ll n,ll m,ll p){
26     if(m==0) return 1;
27     return C(n%p,m%p,p)*lucas(n/p,m/p,p);
28 }
29 #define mod 1000000007
30 int ct[6000]={1,945729344,874271714,728937729,488957151,213941567,621948608,165410919,130152966,477849061,70646122,104331417,804334677,112228257,406385851,373610584,959189339,129232103,596011761,653302265,502350404,254254274,23933464,200023312,437339905,838455202,353529507,181826790,268707842,918554769,361346624,475114772,551764204,264122255,348587014,339775734,190610810,147039338,576212642,958452888,907080272,897468755,485757524,926001334,253159604,720502565,795701677,485379561,512490195,62869610,44647373,170729326,181183678,223602264,14266485,546070015,669748641,266401585,722432477,844276843,806809752,215407850,514089950,48258832,388402233,287386547,184275733,39087220,221157750,796058916,274451201,551481903,468840632,654694122,349643823,123450237,466554578,613371117,104229634,534520804,340376885,53768135,665006362,362834988,113383960,458629513,877935697,990187981,24010351,477599350,491321663,619368665,730486899,302800222,248364522,617385859,136706557,988949479,681384128,140672609,39443745,327846413,353172956,108275948,378351259,482275913,432213793,904945283,871063203,757590126,541675614,649654378,339103071,153511190,307061975,535998427,953278988,315396128,629843192,166102135,623766767,9922024,962639966,258645380,484156059,75913669,837794293,574075634,404396328,768092500,903633183,512519672,44285819,538902069,621789723,71341556,81438997,28847533,40513591,849551327,716939958,942552133,395636757,409774346,383255288,612104482,95851638,696370843,884779483,524922348,220269701,390881347,114227221,395767320,614338019,380172060,180822541,691300228,891829295,967678016,701386253,162940737,994175698,908221589,19098271,438672588,631720803,573850469,339056525,473356393,859071294,949727021,98529638,168890563,563975847,7483795,276476730,39489314,514728211,87529508,963753157,380031470,856696972,158703490,515908206,227044626,959511111,993078622,80360936,888779384,323285665,543535546,550763954,601069950,458756853,717452438,141044757,197501322,634124805,238583278,200414323,553793080,66504653,42069842,722598090,913608032,740683059,742050754,961341417,612741304,91785690,526087340,214299335,290988315,920349511,650032143,826861662,655676777,832872230,243503280,428075391,780176613,762279490,958553222,298583588,683539087,245173409,561149407,172900450,994863083,373712992,577710034,676813275,65061172,354158163,474587452,779048700,252731521,513247255,63716789,589280106,300449755,843219077,437936157,617131692,778975010,166446598,341293627,939851882,377019792,974135048,18159888,617899054,824539871,922256819,904951680,298436189,877366713,763013330,69488053,73161945,968841940,502298660,815060335,585478837,52225572,617841877,964952304,864682249,537138023,438032312,507344261,611203109,211965075,510592131,253042462,662211654,306668985,993054101,886017682,550897294,748379779,600811784,662510825,923914254,398819263,459843924,563578785,800110936,890507874,833696238,67588077,662523469,355339772,897895240,326276953,66185485,707119691,543399352,359252814,343020869,435649016,326479513,313711009,180736295,933688638,341979700,832484396,852821336,938966456,327938691,897898594,514258765,67631305,832209634,147167201,933864871,764372915,290610995,894446445,552066969,955550128,899538317,98587581,791520663,371485442,250166899,386277652,850700239,24883422,365069578,542759096,393648297,338311897,998392022,963038213,184331347,216025562,616142588,243671535,922469047,642896156,173840546,617065897,502916270,399859525,626708892,203438585,794335044,466847771,485435744,176762177,370414892,387922877,421040690,506803021,831791096,536761402,659624740,205742555,354512880,992080290,655638247,441557017,45234385,602453687,642559130,907907516,150309994,959349261,667245533,336984599,7514180,293021893,527065808,716061908,183191397,64976751,577967909,833760679,814950379,238991246,714290102,902231891,437427307,149073027,103173270,685925477,694198173,725256565,71168984,261760780,55757530,112359206,436686978,516723667,537954237,916255072,34043384,456908325,881291767,146092388,189805926,498850664,471576564,977024064,502710283,230937450,166248501,100683033,725464484,750575586,525293805,107750423,541103694,100780834,184498203,767490572,317419646,113029816,182757677,138614676,694365799,832641460,450632411,301670090,972578606,809851941,356139480,741575534,319109663,491688831,946837771,820876500,944731056,441691410,439779726,878100434,110259934,781810231,822737100,122949140,185157201,147977057,78103215,98159640,570747872,913214189,526507036,614910594,606219102,234699129,882201646,184318349,623751699,220799331,756153289,390599249,416019375,679472812,608212465,946818526,676784388,848462543,701625645,631586665,279738981,507735946,983863013,797150469,667058957,302361878,11123699,265956565,759232458,630434107,603234456,651468455,184824418,604726700,101186449,24954474,873710205,172883575,299713548,965606121,589841373,782619807,545740664,94087806,846145323,99057958,275906334,98324641,712417499,506415720,153372884,988856645,995466415,137196894,296743168,461577383,447394859,350928543,800328411,35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31 ll Pow(ll a, ll b)
32 {
33     ll sum = 1;
34     while(b)
35     {
36         if(b%2)
37             sum = sum*a%mod;
38         a = a*a%mod;
39         b /= 2;
40     }
41     return sum;
42 }
43 int main(){
44     int t=1;
45     char s[123456];
46     ll m,n,ans;
47     while(~scanf("%d",&t)){
48         while(t--){
49             scanf("%lld%s",&n,s);
50             m=strlen(s);
51             //cout<<m<<endl;
52             if(m>n||n&1){
53                 printf("0\n");
54             }else{
55                 ans=(n-m)/2;
56                 if(ans<=4999999){
57                     printf("%lld\n",lucas(2*ans+1,ans,1e9+7));
58                 }else{
59                     int i=1;
60                     ans+=1;
61                     for(i=1;i<=5000;i++){
62                         if(i*100000>ans){
63                             break;
64                         }
65                     }
66                     i-=1;
67                    // cout<<i<<endl;
68                     ll now=ct[i];
69                     for(int j=i*100000+1;j<=ans;j++){
70                       //  cout<<"B"<<endl;
71                         now = 2*(2*j-1)*now%mod*Pow(j+1, mod-2)%mod;
72                     }
73                     ll x=now%mod*(((ans+1)%mod*500000004)%mod)%mod;
74                     cout<<x<<endl;
75                 }
76             }
77         }
78     }
79     return 0;
80 }