POJ 3070 Fibonacci (矩阵幂运算)
2017-10-03 15:59
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Time limit
1000 ms
Memory limit
65536 kB
![](http://poj.org/images/3070_1.png)
Given an integer n, your goal is to compute the last 4 digits of Fn.
Input
Output
Sample Input
Sample Output
Hint
![](http://poj.org/images/3070_2.png)
![](http://poj.org/images/3070_3.gif)
思路:矩阵快速幂+对10000取余。
代码:
1000 ms
Memory limit
65536 kB
In the Fibonacci integer sequence, F0 = 0, F1 = 1, and Fn = Fn − 1 + Fn − 2 for n ≥ 2. For example, the first ten terms of the Fibonacci sequence are: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, … An alternative formula for the Fibonacci sequence is
![](http://poj.org/images/3070_1.png)
Given an integer n, your goal is to compute the last 4 digits of Fn.
Input
The input test file will contain multiple test cases. Each test case consists of a single line containing n (where 0 ≤ n ≤ 1,000,000,000). The end-of-file is denoted by a single line containing the number −1.
Output
For each test case, print the last four digits of Fn. If the last four digits of Fn are all zeros, print ‘0’; otherwise, omit any leading zeros (i.e., print Fn mod 10000).
Sample Input
0 9 999999999 1000000000 -1
Sample Output
0 34 626 6875
Hint
As a reminder, matrix multiplication is associative, and the product of two 2 × 2 matrices is given by
![](http://poj.org/images/3070_2.png)
Also, note that raising any 2 × 2 matrix to the 0th power gives the identity matrix:
![](http://poj.org/images/3070_3.gif)
思路:矩阵快速幂+对10000取余。
代码:
#include <cstdio> #include <iostream> #include <algorithm> #include <cmath> #include <cstring> using namespace std; struct Matrix // 定义矩阵 { int a[2][2]; Matrix() { memset(a,0,sizeof(a)); } }; Matrix mul(Matrix a,Matrix b)//矩阵乘法+取余 { Matrix ans; for(int i=0; i<2; i++) { for(int k=0; k<2; k++) { if(a.a[i][k]) for(int j=0; j<2; j++) { ans.a[i][j]+=a.a[i][k]*b.a[k][j]; if(ans.a[i][j]>=10000) ans.a[i][j]%=10000; } } } return ans; } int Mypow(int N) { Matrix mid,re; mid.a[0][0] = mid.a[1][1] = 1; re.a[0][0] = re.a[1][0] = re.a[0][1] = 1; while(N) { if(N&1)mid = mul(mid,re); re = mul(re,re); N >>= 1; } return mid.a[0][1]; } int main() { int N; while(scanf("%d",&N) && N!=-1) { if(N == 0) { printf("0\n"); continue; } else if(N<3) { printf("1\n"); continue; } printf("%d\n",Mypow(N)); } return 0; }
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