Let's define the Fibonacci sequence (F_1,F_2,dots) as (F_1=1,F_2=2,F_i=F_{i-1}+F_{i-2}) ((igeq 3)).
It's well known that every positive integer (x) has its unique Fibonacci representation ((b_1,b_2,dots,b_n)) such that:
· (b_1 imes F_1+b_2 imes F_2+dots+b_n imes F_n=x).
· (b_n=1), and for each (i) ((1leq i<n)), (b_iin{0,1}) always holds.
· For each (i) ((1leq i<n)), (b_i imes b_{i+1}=0) always holds.
For example, (4=(1,0,1)), (5=(0,0,0,1)), and (20=(0,1,0,1,0,1)) because (20=F_2+F_4+F_6=2+5+13).
There are two positive integers (A) and (B) written in Fibonacci representation, Skywalkert calculated the product of (A) and (B) and written the result (C) in Fibonacci representation. Assume the Fibonacci representation of (C) is ((b_1,b_2,dots,b_n)), Little Q then selected a bit (k) ((1leq k<n)) such that (b_k=1) and modified (b_k) to (0).
It is so slow for Skywalkert to calculate the correct result again using Fast Fourier Transform and tedious reduction. Please help Skywalkert to find which bit (k) was modified.
Input
The first line of the input contains a single integer (T) ((1 leq T leq 10\,000)), the number of test cases.
For each case, the first line of the input contains the Fibonacci representation of (A), the second line contains the Fibonacci representation of (B), and the third line contains the Fibonacci representation of modified (C).
Each line starts with an integer (n), denoting the length of the Fibonacci representation, followed by (n) integers (b_1,b_2,dots,b_n), denoting the value of each bit.
It is guaranteed that:
· (1leq |A|,|B|leq 1\,000\,000).
· (2leq |C|leq |A|+|B|+1).
·(sum |A|,sum |B|leq 5\,000\,000).
Output
For each test case, output a single line containing an integer, the value of (k).
Sample Input
1
3 1 0 1
4 0 0 0 1
6 0 1 0 0 0 1
Sample Output
4
学习一波QAQ
整体的思路大概就是设modify的是第k位，那么有：(A imes B=C+F_k)，移项后可得：(F_k=A imes B -C)，预处理出斐波那契数列后直接查找即可。但是注意到A,B都在1e6级别，这个范围有点大，因此需要找一个模数P，使得Fib[1]~Fib[2e6]这个范围内的元素模P两两不同余（为啥是Fib[2e6]呢？因为k的范围最大到2e6）。题解很巧妙地用了自然溢出，即P取unsigned long long的最大值(2^{64})。
（题目里说不会有连续的1，又注意到这个数列是斐波那契数列，因此这个条件的含义就是一个数不会有其他的表示方法，比如（1110）和（1001）的值是一样的，而前者有连续的1，就不会出现在输入中。但这...会产生影响吗..）
正常的Hash参照大佬博客：https://www.cnblogs.com/stelayuri/p/13367956.html 可以用进阶map也可以用双Hash避免冲突。
#include <bits/stdc++.h>
using namespace std;
unsigned long long fib[2000005], A, B, C, k;
int main()
{
int t;
cin >> t;
fib[1] = 1, fib[2] = 2;
for(int i = 3; i <= 2000000; i++) fib[i] = fib[i - 1] + fib[i - 2];
while(t--)
{
int na, nb, nc;
A = B = C = 0;
cin >> na;
for(int i = 1; i <= na; i++)
{
int temp = 0;
scanf("%d", &temp);
if(temp) A += fib[i];
}
cin >> nb;
for(int i = 1; i <= nb; i++)
{
int temp = 0;
scanf("%d", &temp);
if(temp) B += fib[i];
}
cin >> nc;
for(int i = 1; i <= nc; i++)
{
int temp = 0;
scanf("%d", &temp);
if(temp) C += fib[i];
}
k = A * B - C;
for(int i = 1; i <= 2000000; i++)
{
if(fib[i] == k)
{
cout << i << endl;
break;
}
}
}
return 0;
}