I made a simple recursion program for this question http://www.spoj.com/problems/COINS/, but whenever recursion happens my class variables lose their value and store the value from the recursion loop.
Here's the code:
#include<iostream>
using namespace std;
class a
{
public:
int c = 0, d = 0, b = 0, x = 0;
int recur(int n)
{
b = (n / 2);
if (b >= 12)
{
b = recur(b);
}
c = (n / 3);
if (c >= 12)
{
c = recur(c);
}
d = (n / 4);
if (d >= 12)
{
d = recur(d);
}
x = b + c + d;
return x;
}
};
int main()
{
int n;
while(cin)
{
cin >> n;
int b = 0, r = 0;
a abc;
r = (n > abc.recur(n)) ? (n) : (abc.recur(n));
cout << r << endl;
}
return 0;
}
So for input 12, I'll be getting 13 but for the input value of 44 I'm getting 44.
This could be a working solution:
#include <iostream>
using namespace std;
int changeToDollars(int bytelandians) {
int byTwo = bytelandians / 2;
int byThree = bytelandians / 3;
int byFour = bytelandians / 4;
int sum = byTwo + byThree + byFour;
if (sum < bytelandians) {
return bytelandians;
} else {
return changeToDollars(byTwo) + changeToDollars(byThree) + changeToDollars(byFour);
}
}
int main() {
int bytelandians;
cout << "How much bytelandians?: ";
while (cin >> bytelandians) {
cout << "Corresponding $: " << changeToDollars(bytelandians) << endl;
cout << "How much bytelandians?: ";
}
return 0;
}
The changeToDollars function, using a simple recursive algorithm, exchanges each single Byteland coin into the corresponding three ones with minor value, until the overall converted amount is advantageous.
Related
My code:
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int BinaryToDecimal(int n)
{
int ans = 0;
int x = 1;
while (n > 0)
{
int y = n % 10;
ans = ans + x * y;
x = x * 2;
n = n / 10;
}
return ans;
}
int DecimalToBinary(int num)
{
vector<int> vect;
while (num > 0)
{
vect.push_back(num % 2);
num = num / 2;
}
int s = vect.size();
int i = s - 1;
for (i = s - 1; i >= 0; i--)
{
cout << vect.at(i);
}
return vect.at(i);
}
int main()
{
int a, b;
cout << "Enter first number: " << endl;
cin >> a;
cout << "Enter second number: " << endl;
cin >> b;
int a_deci = BinaryToDecimal(a);
int b_deci = BinaryToDecimal(b);
int sum = a_deci + b_deci;
DecimalToBinary(sum);
cout << endl;
return 0;
}
Output:
Enter first number:
10101
Enter second number:
11010
101111terminate called after throwing an instance of 'std::out_of_range'what(): vector::_M_range_check: __n (which is 18446744073709551615) >= this->size() (which is 6)
What does this error message mean and how do I fix it?
After this for loop
for (i = s - 1; i >= 0; i--)
{
cout << vect.at(i);
}
the variable i is equal to -1.
So the next call of the member function at with the value equal to -1 (that yields a very big number of the unsigned type std::vector<int>::size_type)
return vect.at(i);
throws the exception.
It seems you need to return from the function the whole vector elements of which will represent a number in the binary form.
Instead of the container std::vector<int> it will be better to use std::bitset.
This is what I came up with
#include <iostream>
using namespace std;
int serialNumber = 1;
Would recursion be better?
int factorial(int n)
{
int k=1;
for(int i=1;i<=n;++i)
{
k=k*i;
}
return k;
}
How can I go about doing this in a single for loop?
Or is this the best way?
int main()
{
int a;
int b;
int c;
int fact1;
int fact2;
int fact3;
for (a=1;a < 11;a++)
{
fact1 = factorial(a);
for (b=1;b < 11;b++)
{
fact2 = factorial(b);
for (c=1;c < 11;c++)
{
fact3 = factorial(c);
cout << serialNumber << " : ";
int LHS = fact1 + fact2 + fact3;
if (LHS == a * b * c)
{
cout << "Pass:" <<" "<< a << " & " << b << " & " << c << endl;
}
else
{
cout << "Fail" <<endl;
}
serialNumber++;
}
c = 1;
}
b = 1;
}
return 0;
}
I am being forced to add more none code into it.
Thanks for the help!
Don't know if this is helps,but>
check for minimum of A,B,C
A!+B!+C! = (min(A,B,C)!)*(1+((min+1..restfact1)!)+((min+1..restfact2)!))
So, you can calculate the minimum factorial and than re-use it for calculating others.
On the other hand, you can calculate only the maximum factorial and store its results in the array, and re-use pre-calculated values for finding factorial of smaller numbers
Other implication is that the minimum number can be reduced
restfact1 * restfact2 = ((min-1)!)*(1+((min+1..restfact1)!)+((min+1..restfact2)!))
Part of the question was how can this be done in a single loop and this is one way to do that.
I don't think this is a better way of doing it, but the question was asked:
constexpr int bound = 10;
int Factorials[bound + 1];
for (int i = 1; i <= bound; ++i) Factorials[i] = Factorial(i);
for (int i = 0; i < bound * bound * bound; ++i) {
int s = i + 1;
int a = i;
int c = 1 + a % bound;
a /= bound;
int b = 1 + a % bound;
a /= bound;
++a;
cout << s << " : ";
int LHS = Factorials[a] + Factorials[b] + Factorials[c];
if (LHS == a * b * c)
...
}
I have written the code for RSA in C++ on Ubuntu. It was working fine on that, it's working fine on Windows Dev C++ as well, but it doesn't show the character properly.
Here is the code :
#include<iostream>
#include<stdlib.h> // for rand()
#include<math.h> // for floor function
#include<string.h>
using namespace std;
//function to check whether a number is prime or not
int check_prime(int number)
{
int count = 0;
for(int i = 2; i<number + 1; i++)
{
if(number%i == 0)
{
count++;
}
}
if(count>2)
{
return 0;
}
else
{
return 1;
}
}
//function to generate a random prime number
int generate_random_prime()
{
int temp;
while(1)
{
temp = rand() % 50;
if(check_prime(temp) == 1)
{
return temp;
}
}
}
int gcd(int a, int b)
{
int temp;
while(b != 0)
{
temp = b;
b = a%b;
a = temp;
}
return a;
}
// Extended Euclid GCD to find d such de congruent to 1
int extended_gcd(int a, int b)
{
int d, x, y, r, q;
if(b == 0)
{
d = a;
x = 1;
y = 0;
cout << "\n d= " << d << " x= " << x << " y= " << y << "\n";
}
int x2, x1, y2, y1;
x2 = 1;
x1 = 0;
y2 = 0;
y1 = 1;
while(b > 0)
{
q = floor(a / b);
r = a - q*b;
x = x2 - q*x1;
y = y2 - q*y1;
a = b;
b = r;
x2 = x1;
x1 = x;
y2 = y1;
y1 = y;
}
d = a;
x = x2;
y = y2;
return x2;
}
//returns a^b mod n using square and multiply method
int modular_exponentiation(int a, int b, int n)
{
if(a == 1)
{
return 0;
}
int c = 1;
for(int i = 1; i < b + 1; i++)
{
c = (c*a) % n;
}
return c;
}
//cipher text = (message^e) %n
int cipher_text(int m, int e, int n)
{
return modular_exponentiation(m, e, n);
}
//decrypted_text= (cipher^d)%n
int decrypt_cipher(int c, int d, int n)
{
return modular_exponentiation(c, d, n);
}
int main()
{
// generating two random prime p and q
int p = generate_random_prime();
int q = generate_random_prime();
cout << "Prime p : " << p << "and q : " << q << "\n";
int n = p*q;
cout << "n=p*q = " << n << "\n";
//calculating Euler Totient for prime p and q
int euler_phi = (p - 1)*(q - 1);
cout << "Euler totient is : " << euler_phi << "\n";
int d, e;
// calculating e such that 1<e<euler_phi and gcd(n,euler_phi)=1
while(1)
{
e = rand() % (euler_phi - 1 + 1) + 1;
if(gcd(euler_phi, e) == 1)
{
break;
}
}
cout << "e value is : " << e << "\n";
//calculating d such that ed congruent 1, ed=1
d = extended_gcd(e, euler_phi);
//d=5;
cout << "d value is : " << d << "\n";
//storing the message to be encrypted as char array and encrypting each char element
char message[20];
int cipher[20];
cout << "Enter the message to be encrypted : ";
cin >> message;
cout << "Message to be encrypted is : " << message << "\n";
int size = strlen(message);
//calculating cipher text c
for(int i = 0; i < size; i++)
{
cipher[i] = cipher_text(int(message[i]), e, n);
}
cout << "Cipher text is : ";
for(int i = 0; i < size; i++)
{
cout << cipher[i] << " ";
}
char message_decrypted[size];
//decrypting cipher text
for(int i = 0; i < size; i++)
{
message_decrypted[i] = decrypt_cipher(cipher[i], d, n);
}
cout << "\nDecrypted message is : ";
for(int i = 0; i < size; i++)
{
cout << message_decrypted[i];
}
cout << "\n";
return 0;
}
I have tried the code on DevC++ and using g++.
Check the images :
Image using g++ compiler
I need a way to print the char to be displayed properly.
I think that message_decrypted[i]=decrypt_cipher(cipher[i],d,n); needs to be changed to print the character properly in Devcpp
Here is the link to the code in online IDE where it works fine https://repl.it/#shubhamjohar/RSA
When your main routine invokes
decrypt_cipher(cipher[i], d, n);
cipher[0] is 386 as matching your output above. d is -179. And n is 697
The corresponding call into modular_exponentiation(a=386, b=-179, n=697) results in this for-loop getting skipped:
for (int i = 1; i<b + 1; i++) {
c = (c*a) % n;
}
Because i < (b + 1) evaluates to (1 < -178), which evaluates to false.
Therefore, your modular_exponentiation returns 1, which is an unprintable character.
Same applies for the subsequent calls to decrypt_cipher from main.
I don't know enough about the RSA algorithm to know if your implementation is correct. But when d is negative, that for-loop isn't going to do any loops.
Maybe it is incurred by the following expression in your program:
char message_decrypted[size];
There is some standard change related to this usage. please read the following page for more details.
https://www.geeksforgeeks.org/variable-length-arrays-in-c-and-c/
Or try to use something like new char[size] to allocate memory dynamically.
I am trying to do an exercise with the Fibonacci series.
I have to implement with a recursive function, a succession of the prime n number of Fibonacci and print them
in the same function. The problem is that my function print also the intermediate number.
The results, for example, for n = 6, should be : 1 1 2 3 5 8.
Any solutions?
Thanks
#include<iostream>
using namespace std;
int rec(int n)
{
int a, b;
if (n == 0 || n == 1)
{
return n;
}
else
{
a = rec(n - 1);
b = rec(n - 2);
cout << a + b << endl;
return a + b;
}
}
int main()
{
int n = 6;
rec(n);
return 0;
}
I have taken help of static int. That worked the way you wanted.
void rec(int n)
{
static int a=0,b=1,sum;
if(n>0)
{
sum = a+b;
a=b;
b= sum;
cout<<sum<<" ";
rec(n-1);
}
}
Though you have to print the first Fibonacci number yourself in main().
cout<<"0 ";
rec(n);
You can use this:
#include<iostream>
using namespace std;
#define MAXN 100
int visited[MAXN];
int rec(int n)
{
if(visited[n])
{
return visited[n];
}
int a, b;
if (n == 0|| n==1)
{
return n;
}
else
{
a = rec(n - 1);
b = rec(n - 2);
cout << " " <<a + b;
return visited[n] = a + b;
}
}
int main()
{
int n = 6;
cout<< "1";
rec(n);
cout<<endl;
return 0;
}
This implementation uses dynamic programming. So it reduces the computation time :)
Because you are printing in rec, its printing multiple times because of recursion. No need to print in the recursive function. Instead print the result in main
#include<iostream>
using namespace std;
int rec(int n)
{
int a, b;
if (n == 0 || n == 1)
{
return n;
}
else
{
a = rec(n - 1);
b = rec(n - 2);
//cout << a + b << endl;
return a + b;
}
}
int main()
{
int n = 6;
for (int i = 1; i <= n; i++)
{
cout << rec(i) << endl;
}
system("pause");
return 0;
}
I'm pretty sure you have gotten working solutions but I have a slightly different approach that doesn't require you to use data structures:
/* Author: Eric Gitangu
Date: 07/29/2015
This program spits out the fibionacci sequence for the range of 32-bit numbers
Assumption: all values are +ve ; thus unsigned int works here
*/
#include <iostream>
#include <math.h>
#define N pow(2.0,31.0)
using namespace std;
void fibionacci(unsigned int &fib, unsigned int &prevfib){
unsigned int temp = prevfib;
prevfib = fib;
fib += temp;
}
void main(){
int count = 0;
unsigned int fib = 0u, prev = 1u;
while(fib < N){
if( fib ==0 ){
fib = 0;
cout<<" "<< fib++ <<" \n ";
continue;
}
if( fib == 1 && count++ < 2 ){
fib = 1;
cout<< fib <<" \n ";
continue;
}
fibionacci(fib, prev);
cout<< fib <<" \n ";
}
}
Try this recursive function.
int fib(int n)
return n<=2 ? n : fib(n-1) + fib(n-2);
It is the most elegant solution I know.
I've tried to solve a coin change problem in such a way that it'll compute the minimum numbers of coins that can be used. I've used the algorithm post on http://www.algorithmist.com. Here's the algorithm:
C(N,m) = min(C(N,m - 1),C(N - Sm,m) + 1)
with the base cases:
C(N,m) = 1,N = 0
C(N,m) = 0,N < 0
C(N, m) = 0, N >= 1, m <= 0
But when I write the code it run to infinity.
Here's the code:
#include <iostream>
#include <algorithm>
using namespace std;
int Types[101];
int Coins(int N, int m)
{
if(N==0)
{
return 1;
}
else if(N<0)
{
return 0;
}
else if(N>0 && m<=0)
{
return 0;
}
else
{
int a = Coins(N,m-1);
int b = Coins(N-Types[m],m) + 1;
int c = min(a,b);
return c;
}
}
int main()
{
int noOfCoins, Target;
cin >> noOfCoins >> Target;
for(int i = 0; i<noOfCoins; i++)
{
cin >> Types[i];
}
cout << Coins(Target, noOfCoins);
return 0;
}
What can be wrong?
It should be cout << Coins(Target, noOfCoins - 1);
instead of cout << Coins(Target, noOfCoins);
Otherwise you are accessing a 0 element, and go to the same state again and again here:
int b = Coins(N-Types[m],m) + 1;