Everybody knows Fibonacci numbers, now we are talking about the Tribonacci numbers:
T[0] = T[1] = T[2] = 1;
T[n] = T[n - 1] + T[n - 2] + T[n - 3] (n >= 3)
Given a and b, you are asked to calculate the sum from the ath Fibonacci number to the bth Fibonacci number, mod 1,000,000,007, that is (T[a] + T[a + 1] + ... + T[b]) % 1,000,000,007.
#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
;
;
__int64 N;
void multipy( __int64 a[MAX_N][MAX_N], __int64 b[MAX_N][MAX_N], __int64 c[MAX_N][MAX_N] ){
; i <= ; i++ ){
; j <= ; j++ ){
c[i][j] = ;
; k <= ; k++ ){
c[i][j] = ( c[i][j] + a[i][k] * b[k][j] % MOD ) % MOD;
}
}
}
}
void get_matrix_pow( __int64 a[MAX_N][MAX_N], __int64 n ){
__int64 ans[MAX_N][MAX_N] = {};
__int64 temp[MAX_N][MAX_N];
; i <= ; i++ ) ans[i][i] = ;
while( n ){
== ){
multipy( ans, a, temp );
memcpy( ans, temp, sizeof( __int64 ) * MAX_N * MAX_N );
}
multipy( a, a, temp );
memcpy( a, temp, sizeof( __int64 ) * MAX_N * MAX_N );
n /= ;
}
memcpy( a, ans, sizeof( __int64 ) * MAX_N * MAX_N );
}
__int64 solve( __int64 n ){
__int64 a[MAX_N][MAX_N] = {};
){
;
}
){
;
} ){
;
}
a[][] = ;a[][] = ;a[][] = ;a[][] = ;
a[][] = ;a[][] = ;a[][] = ;a[][] = ;
a[][] = ;a[][] = ;a[][] = ;a[][] = ;
a[][] = ;a[][] = ;a[][] = ;a[][] = ;
get_matrix_pow( a, n - );
__int64 ans = ;
__int64 b[MAX_N];
b[] = b[] = b[] = ;
b[] = ;
; i <= ; i++ ){
ans = ( ans + a[][i] * b[i] % MOD ) % MOD;
}
return ans;
}
int main(){
__int64 A, B;
while( scanf( "%I64d%I64d", &A, &B ) != EOF ){
printf( ) + MOD ) % MOD );
}
;
}