Kirai[HDOJ6084] 寻找母串（分块打表，递推）
题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=6084
这题打表找规律，发现答案是：
打表代码：
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 const int maxn = 11; 5 int n, p[maxn], v[maxn]; 6 7 bool ok() { 8 int one = 0, zero = 0; 9 for(int i = 1; i <= n; i++) { 10 if(v[i] == 1) one++; 11 else zero++; 12 if(zero > one) return 0; 13 } 14 return zero == one; 15 } 16 17 signed main() { 18 // freopen("in", "r", stdin); 19 while(~scanf("%d", &n)) { 20 int nn = 1 << n; 21 int cnt = 0; 22 for(int i = 0; i < nn; i++) { 23 for(int j = 0; j < n; j++) { 24 if((1 << j) & i) v[j+1] = 1; 25 else v[j+1] = 0; 26 } 27 if(!ok()) continue; 28 // for(int i = 1; i <= n; i++) printf("%d", v[i]); 29 // printf("\n"); 30 for(int i = 4; i <= n; i++) { 31 if(v[i-3] == 1 && v[i-2] == 0 && v[i-1] == 1 && v[i] == 0) cnt++; 32 } 33 } 34 printf("%d\n", cnt); 35 } 36 return 0; 37 }
之后发现这个阶乘怎么这！么！大！
而后阶乘再打个表，跑不到一分钟就能跑出来。
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 typedef long long LL; 5 const int sz = 1000000; 6 const LL mod = (LL)1e9+7; 7 8 int main() { 9 freopen("out", "w", stdout); 10 LL t = 0; 11 for(int i = 0; i < mod; i++) { 12 if(i == 0) t = 1; 13 else t = t * (LL)i % mod; 14 if(i % sz == 0) printf("%lld,", t); 15 } 16 return 0; 17 }
ac代码：
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 typedef long long LL; 5 const int maxn = 1000100; 6 const LL mod = (LL)1e9+7; 7 const LL f[maxn] = {1,641102369,578095319,5832229,259081142,974067448,316220877,690120224,251368199,980250487,682498929,134623568,95936601,933097914,167332441,598816162,336060741,248744620,626497524,288843364,491101308,245341950,565768255,246899319,968999,586350670,638587686,881746146,19426633,850500036,76479948,268124147,842267748,886294336,485348706,463847391,544075857,898187927,798967520,82926604,723816384,156530778,721996174,299085602,323604647,172827403,398699886,530389102,294587621,813805606,67347853,497478507,196447201,722054885,228338256,407719831,762479457,746536789,811667359,778773518,27368307,438371670,59469516,5974669,766196482,606322308,86609485,889750731,340941507,371263376,625544428,788878910,808412394,996952918,585237443,1669644,361786913,480748381,595143852,837229828,199888908,526807168,579691190,145404005,459188207,534491822,439729802,840398449,899297830,235861787,888050723,656116726,736550105,440902696,85990869,884343068,56305184,973478770,168891766,804805577,927880474,876297919,934814019,676405347,567277637,112249297,44930135,39417871,47401357,108819476,281863274,60168088,692636218,432775082,14235602,770511792,400295761,697066277,421835306,220108638,661224977,261799937,168203998,802214249,544064410,935080803,583967898,211768084,751231582,972424306,623534362,335160196,243276029,554749550,60050552,797848181,395891998,172428290,159554990,887420150,970055531,250388809,487998999,856259313,82104855,232253360,513365505,244109365,1559745,695345956,261384175,849009131,323214113,747664143,444090941,659224434,80729842,570033864,664989237,827348878,195888993,576798521,457882808,731551699,212938473,509096183,827544702,678320208,677711203,289752035,66404266,555972231,195290384,97136305,349551356,785113347,83489485,66247239,52167191,307390891,547665832,143066173,350016754,917404120,296269301,996122673,23015220,602139210,748566338,187348575,109838563,574053420,105574531,304173654,542432219,34538816,325636655,437843114,630621321,26853683,933245637,616368450,238971581,511371690,557301633,911398531,848952161,958992544,925152039,914456118,724691727,636817583,238087006,946237212,910291942,114985663,492237273,450387329,834860913,763017204,368925948,475812562,740594930,45060610,806047532,464456846,172115341,75307702,116261993,562519302,268838846,173784895,243624360,61570384,481661251,938269070,95182730,91068149,115435332,495022305,136026497,506496856,710729672,113570024,366384665,564758715,270239666,277118392,79874094,702807165,112390913,730341625,103056890,677948390,339464594,167240465,108312174,839079953,479334442,271788964,135498044,277717575,591048681,811637561,353339603,889410460,839849206,192345193,736265527,316439118,217544623,788132977,618898635,183011467,380858207,996097969,898554793,335353644,54062950,611251733,419363534,965429853,160398980,151319402,990918946,607730875,450718279,173539388,648991369,970937898,500780548,780122909,39052406,276894233,460373282,651081062,461415770,358700839,643638805,560006119,668123525,686692315,673464765,957633609,199866123,563432246,841799766,385330357,504962686,954061253,128487469,685707545,299172297,717975101,577786541,318951960,773206631,306832604,204355779,573592106,30977140,450398100,363172638,258379324,472935553,93940075,587220627,776264326,793270300,291733496,522049725,579995261,335416359,142946099,472012302,559947225,332139472,499377092,464599136,164752359,309058615,86117128,580204973,563781682,954840109,624577416,895609896,888287558,836813268,926036911,386027524,184419613,724205533,403351886,715247054,716986954,830567832,383388563,68409439,6734065,189239124,68322490,943653305,405755338,811056092,179518046,825132993,343807435,985084650,868553027,148528617,160684257,882148737,591915968,701445829,529726489,302177126,974886682,241107368,798830099,940567523,11633075,325334066,346091869,115312728,473718967,218129285,878471898,180002392,699739374,917084264,856859395,435327356,808651347,421623838,105419548,59883031,322487421,79716267,715317963,429277690,398078032,316486674,384843585,940338439,937409008,940524812,947549662,833550543,593524514,996164327,987314628,697611981,636177449,274192146,418537348,925347821,952831975,893732627,1277567,358655417,141866945,581830879,987597705,347046911,775305697,125354499,951540811,247662371,343043237,568392357,997474832,209244402,380480118,149586983,392838702,309134554,990779998,263053337,325362513,780072518,551028176,990826116,989944961,155569943,596737944,711553356,268844715,451373308,379404150,462639908,961812918,654611901,382776490,41815820,843321396,675258797,845583555,934281721,741114145,275105629,666247477,325912072,526131620,252551589,432030917,554917439,818036959,754363835,795190182,909210595,278704903,719566487,628514947,424989675,321685608,50590510,832069712,198768464,702004730,99199382,707469729,747407118,302020341,497196934,5003231,726997875,382617671,296229203,183888367,703397904,552133875,732868367,350095207,26031303,863250534,216665960,561745549,352946234,784139777,733333339,503105966,459878625,803187381,16634739,180898306,68718097,98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8 char s[maxn]; 9 const int sz = 1000000; 10 LL n, m; 11 12 LL F(int n) { 13 LL ret = f[n/sz]; 14 for(int i = (n / sz) * sz + 1LL; i <= n; i++) { 15 ret = ret * i % mod; 16 } 17 return ret; 18 } 19 20 LL exgcd(LL a, LL b, LL &x, LL &y) { 21 if(b == 0) { 22 x = 1; 23 y = 0; 24 return a; 25 } 26 else { 27 LL ret = exgcd(b, a%b, x, y); 28 LL tmp = x; 29 x = y; 30 y = tmp - a / b * y; 31 return ret; 32 } 33 } 34 35 LL inv(LL a) { 36 LL x, y; 37 exgcd(a, mod, x, y); 38 return (x % mod + mod) % mod; 39 } 40 41 LL C(LL n) { 42 return (F(2LL*n+1) * inv(F(n+1)) % mod) * inv(F(n)); 43 } 44 45 signed main() { 46 // freopen("in", "r", stdin); 47 int T; 48 scanf("%d", &T); 49 while(T--) { 50 scanf("%I64d %s", &n, s); 51 m = (LL)strlen(s); 52 if(n < m) { printf("0\n"); continue; } 53 if(n % 2 || m % 2) { printf("0\n"); continue; } 54 LL p = (n - m) / 2; 55 printf("%I64d\n", C(p)%mod); 56 } 57 return 0; 58 }
