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Create Fibonacci Sum.cpp #5

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50 changes: 50 additions & 0 deletions Coding Exercise Solutions/Fibonacci Sum.cpp
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Original file line number Diff line number Diff line change
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#include<bits/stdc++.h>
using namespace std;
#define mod 1000000007

void multiply(vector<vector<long long>>& F, vector<vector<long long>>&M)
{
long long x,y,z,w;
x = (F[0][0]*M[0][0] + F[0][1]*M[1][0])%mod;
y = (F[0][0]*M[0][1] + F[0][1]*M[1][1])%mod;
z = (F[1][0]*M[0][0] + F[1][1]*M[1][0])%mod;
w = (F[1][0]*M[0][1] + F[1][1]*M[1][1])%mod;

F[0][0] = x;
F[0][1] = y;
F[1][0] = z;
F[1][1] = w;
}

void power(vector<vector<long long>>&F, int n){
if( n == 0 || n == 1)
return;

vector<vector<long long>>M = {{1,1},{1,0}};

power(F, n/2);
multiply(F, F);

if (n%2 != 0){
multiply(F, M);
}
}

long long fib(long long n)
{
vector<vector<long long>> F= {{1,1},{1,0}};
if (n == 0){
return 0;
}
power(F, n-1);
return F[0][0];
}

int fibSum(int n,int m){
int ans=(fib(m+2)-fib(n+1))%mod;
if(ans<0){
ans+=mod;
}
return ans;
}