Moamen and XOR (位運算+組合數+取模+逆元+dp)
阿新 • • 發佈:2022-04-20
Moamen and Ezzat are playing a game. They create an array aa of nn non-negative integers where every element is less than 2^k2 k . Moamen wins if a_1 \,\&\, a_2 \,\&\, a_3 \,\&\, \ldots \,\&\, a_n \ge a_1 \oplus a_2 \oplus a_3 \oplus \ldots \oplus a_na 1 &a 2 &a 3View problem &…&a n ≥a 1 ⊕a 2 ⊕a 3 ⊕…⊕a n . Here \&& denotes the bitwise AND operation, and \oplus⊕ denotes the bitwise XOR operation. Please calculate the number of winning for Moamen arrays aa. As the result may be very large, print the value modulo 1\,000\,000\,0071000000007 (10^9 + 7109 +7). Input The first line contains a single integer tt (1 \le t \le 51≤t≤5)— the number of test cases. Each test case consists of one line containing two integers nn and kk (1 \le n\le 2\cdot 10^51≤n≤2⋅10 5 , 0 \le k \le 2\cdot 10^50≤k≤2⋅10 5 ). Output For each test case, print a single value — the number of different arrays that Moamen wins with. Print the result modulo1\,000\,000\,0071000000007 (10^9 + 710 9 +7). Sample 1 Inputcopy Outputcopy 3 3 1 2 1 4 0 5 2 1 Note In the first example, n = 3n=3, k = 1k=1. As a result, all the possible arrays are [0,0,0][0,0,0], [0,0,1][0,0,1], [0,1,0][0,1,0], [1,0,0][1,0,0], [1,1,0][1,1,0], [0,1,1][0,1,1], [1,0,1][1,0,1], and [1,1,1][1,1,1]. Moamen wins in only 55 of them: [0,0,0][0,0,0], [1,1,0][1,1,0], [0,1,1][0,1,1], [1,0,1][1,0,1], and [1,1,1][1,1,1].
思路:
- 利用位運算的性質,&有一個0就為0,^看1的奇偶個數,因此 將 把n個數 按照二進位制寫就行了,
- 排在一起,一位一位的看,更具第一點,n為偶數 就有勝利的情況,n為奇數只有平局的情況
- 偶數: DP就行了, DP[0][i] 代表平局 DP[1][i] 代表勝利。 具體轉移看程式碼比較簡單。
- 組合數的處理見程式碼,
- 最後!!!!!!!!!!!!!!!!!!!!!
- 取mod 一定要看 是不是所有式子都取了mod!!!!!!!!!!!!!!!
- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
- 且中間是不是要加%mod,很重要!!!!!
#include <bits/stdc++.h> using namespace std; #define ri register int #define M 200005 template <class G> void read(G &x) { x=0;int f=0;char ch=getchar(); while(ch<'0'||ch>'9'){f|=ch=='-';ch=getchar();} while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();} x=f?-x:x; return ; } const int mod=1e9+7; long long inv[M],inf[M]; long long al[M]; int n,m; long long ksn(long long a,int n) { long long ans=1; while(n) { if(n&1) ans=ans*a%mod; n>>=1;a=a*a%mod; } return ans; } void init() { inv[0]=inf[0]=1; for(ri i=1;i<=2e5;i++) { inf[i]=inf[i-1]*i%mod; inv[i]=inv[i-1]*ksn(i,mod-2)%mod; } al[0]=1; for(ri i=1;i<=2e5;i++) { al[i]=al[i-1]*2%mod; } } long long dp[4][M]; long long zh(int n,int b) { return inf[n]*inv[n-b]%mod*inv[b]%mod; } void sol1() { long long pin=0; for(ri i=0;i<n;i+=2) { pin=(pin+zh(n,i))%mod; } dp[0][1]=pin; dp[1][1]=1; dp[2][1]=1; for(ri i=2;i<=m;i++) { dp[2][i]=al[n]*dp[2][i-1]%mod; // 這個點勝利 其他點 隨便取 dp[1][i]=dp[2][i]; dp[1][i]=(dp[1][i]+pin*(dp[1][i-1])%mod)%mod; dp[0][i]=pin*dp[0][i-1]%mod; } long long ans=(dp[0][m]+dp[1][m])%mod; printf("%lld\n",ans); } void sol2() { long long pin=0; for(ri i=0;i<n;i+=2) { pin=(pin+zh(n,i))%mod; } pin++;long long ans=1; for(ri i=1;i<=m;i++) { ans=ans*pin%mod; } printf("%lld\n",ans); } int main(){ init(); int T; read(T); while(T--) { read(n);read(m); if(m==0) { printf("1\n");continue; } if(n&1) sol2(); else sol1(); } return 0; }View Code