I'm new to objective c and I would like to know if there is a method for greatest common factor
gcf() for example so you get the idea
There's no out of the box function. Since Objective-C is a superset of C, you can grab an existing library or set of functions and include it where necessary.
Based on http://www.idevelopment.info/data/Programming/data_structures/c/gcd/gcd.c, you might do this:
// gcd.h
int gcd(int m, int n);
// gcd.c
int gcd(int m, int n) {
int t, r;
if (m < n) {
t = m;
m = n;
n = t;
}
r = m % n;
if (r == 0) {
return n;
} else {
return gcd(n, r);
}
}
Include that file whenever you should wish to use the gcd function:
#import "gcd.h"
There is no built in method, but the Euclidean algorithm is easy to implement, and quite efficient.
The binary GCD algorithm can be slightly more efficient. This link has C code implementing it.
By far the most elegant solution I have come across (non-recursive of course):
int gcd (int a, int b){
int c;
while ( a != 0 ) {
c = a; a = b%a; b = c;
}
return b;
}
Source.
Just putting damian86's answer into Objective-C style (reference to self assumes context of an object, modify accordingly, you could make this a category, etc):
-(int)greatestCommonDivisorM:(int)m N:(int)n
{
int t, r;
if (m < n) {
t = m;
m = n;
n = t;
}
r = m % n;
if (r == 0) {
return n;
} else {
return [self greatestCommonDivisorM:n N:r];
}
}
Related
What's the Big O notation of the following method and why?
public int f(int n) {
if (n <= 0) {
return 0;
}
return f(n/2) + n;
}
this is a program to multiply 2 matrixes which comes in maths, but dont know why, am getting answers like "-1282230" or some weird numbers. I would like to know what is causing it and how could i fix it? THANK YOU!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
int main()
{
int m[3][3],m2[3][3],i,je,k,ans[3][3],sum;
// taking inputs from the user for matrix1
printf("Enter the numbers for first matrix");
je=0;
for(i=0;i<3;i++){
printf(" for row %d\n",i+1);
for(je=0;je<3;je++){
scanf("%d",&m[i][je]);
}
}
// taking inputs from the user for matrix2
printf("Enter the numbers for second matrix");
je=0;
for(i=0;i<3;i++){
printf(" for row = %d\n",i+1);
for(je=0;je<3;je++){
scanf("%d",&m2[i][je]);
}
}
// multiplication OR MATRIX CMS HERE;
sum = 0;
for(k=0;k<9;k++){
for(i=0;i<3;i++){
for(je=0;je<3;je++){
sum = m[k][je] * m2[je][i];
ans[i][je] = sum;
}
}
k++;
}
// it ENDS;
puts("ANSWER IS:: \n");
// Displaying answer, matrix;
for(i=0;i<3;i++){
for(je=0;je<3;je++){
printf("%d\t",ans[i][je]);
}
printf("\n");
}
return 0;
}
Here's a working solution. One of the problem with your code is that you aren't setting the sum to 0 after each multiplication.
#include <stdio.h>
int main() {
int m, n, p, q, c, d, k, sum = 0; int first[10][10], second[10][10], multiply[10][10];
printf("Enter number of rows and columns of first matrix\n"); scanf("%d%d", &m, &n); printf("Enter elements of first matrix\n");
for (c = 0; c < m; c++)
for (d = 0; d < n; d++)
scanf("%d", &first[c][d]);
printf("Enter number of rows and columns of second matrix\n"); scanf("%d%d", &p, &q);
if (n != p)
printf("The matrices can't be multiplied with each other.\n"); else {
printf("Enter elements of second matrix\n");
for (c = 0; c < p; c++)
for (d = 0; d < q; d++)
scanf("%d", &second[c][d]);
for (c = 0; c < m; c++) {
for (d = 0; d < q; d++) {
for (k = 0; k < p; k++) {
sum = sum + first[c][k]*second[k][d];
}
multiply[c][d] = sum;
sum = 0;
}
}
printf("Product of the matrices:\n");
for (c = 0; c < m; c++) {
for (d = 0; d < q; d++)
printf("%d\t", multiply[c][d]);
printf("\n");
}
}
return 0; }
Hi sorry for my bad english, i have a question guys, i'm learning objective c and i'm learning booleans right now, my question is: why when running the second loop in the code, the number 2 is taken as prime, i mean, as i see it p takes the value 2 in the first loop, then d start at 2 but then it says d < p, i think that's p-1 (2-1 = 1), so how that code works, it doesn't make sense, i understand why it works with any other number greater than 2 but i don't get it why it works with the number 2!
#import <Foundation/Foundation.h>
int main(int argc, const char * argv[]) {
#autoreleasepool
{
int p, d;
BOOL isPrime;
for (p = 2; p <= 50; p++)
{
isPrime = true;
for (d = 2; d < p; d++)
{
if (p % d == 0)
isPrime = false;
}
if (isPrime == true)
NSLog(#"%i", p);
}
}
return 0;
}
The first loop starts p=2, then the inner loop take d=2 and then check if d<p. This condition is false because d=2 P=2. This means the first inner loop doesn't run and isPrime is always true at the first loop of p.
A prime number is divisible by 1 or itself.
So we check divisibility for all the numbers between 1 and the number.
That is why we start we 2 and till number-1
for(d = 2; d < p; d++ )
Prime numbers are the numbers which are not divisible by any other number.They are divisible by itself only (eg 2,3,5,7)
If we will only check till the half of number, since more than half of number will not divide it.
-(BOOL)checkNumberPrimeNumber:(int)number{
int i; BOOL flag=false;
for (i=2; i<number/2; i++) {
if (number%i==0) {
flag=true;
break;
}
}
if (flag==true) {
NSLog(#"%d is Not Prime Number",number);
}
else{
NSLog(#"%d is Prime Number",number);
}
return YES;
}
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ive refined it a bit. Can someone change it to the correct way for me?
i also introduced a new variable isPrime i guess this is a bit better
#import <Foundation/Foundation.h>
int main(int argc, const char * argv[])
{
#autoreleasepool {
int p = 7;
int d, isPrime = 0;
if (p % 2 != 0)
{
for (d = 2; d < p; d++) {
p % d;
}
if (p % d == 0)
{
isPrime = 1; //not prime
}
if (p % d != 0)
{
isPrime = 2; //is prime
}
if (isPrime == 1)
{
NSLog(#"its not prime");
}
if (isPrime == 2) {
NSLog(#"its prime");
}
}
else
NSLog(#"sorry");
}
return 0;
}
There's the well-known Sieve of Eratosthenes, but if you are writing a program that is just going to take one number as input and decide whether it's prime, the Sieve does more than you need (it finds all primes less than some value of your choice) so it may not be your most efficient choice of algorithm.
A couple other things about finding primes:
If you find that p is not even, you only have to try dividing it by odd numbers, that is, 3, 5, 7, 9, etc. (Yes, once you know it's not divisible by 3, technically you know it's not divisible by 9, but it may not be worthwhile or even efficient to account for such things in your algorithm.)
You don't have to try anything larger than sqrt(p) as a divisor. If you haven't found a divisor by then, you never will (except for 1 and p itself).
If you find a number that divides p, you can say immediately that p is not prime. (You might want to make sure you exit any loops then, too, otherwise you might end up printing the announcement that p is not prime more than once.)
... But you must never say that p is prime until the end of your algorithm, after all loops have completed. Until then, the most you can say is you haven't yet found a proof that p is not prime.
Above loop is fine , but you have to start from 3 rather than 2.
This is pseudo code for prime number calculation :
int num = 11;
NSString * res = null;
for(int i = 2 ;i<num ;i ++)
{
if(num%i == 0)
{
res = #"This is not a prime number";
break
}
else{
res = #"This is prime number";
}
}
try this
int p = 7;
int d, isPrime = 2;
if (p % 2 != 0)
{
for (d = 2; (d < p) && (isPrime == 2); d++) {
if (p % d == 0)
{
isPrime = 1; //not prime
}
if (p % d != 0)
{
isPrime = 2; //is prime
}
}
if (isPrime == 1)
{
NSLog(#"its not prime");
}
if (isPrime == 2) {
NSLog(#"its prime");
}
}
else
NSLog(#"sorry");
In Metro Style apps sometimes we use Platform::Collections::Vector to hold elements used in a ListView.
How to sort a Platform::Collections::Vector?
I'm aware there are plenty of structures in std that can be sorted but I was wondering if there was some method for Platform::Collections::Vector other than writing your own sort function.
Actually something like the below should also work:
auto vec = ref new Platform::Collections::Vector<T^>();
std::sort(begin(vec), end(vec));
I didn't find any suitable answer so I used this workaround.
It's a simple quicksort over a Platform::Collections::Vector
void swap (Platform::Collections::Vector<T^>^ vec, int pos1, int pos2)
{
T^ tmp = vec->GetAt(pos1);
vec->SetAt(pos1, vec->GetAt(pos2));
vec->SetAt(pos2,tmp);
}
int compare (T^ c1, T^ c2)
{
int c = wcscmp (c1->Title->Data(),c2->Title->Data());
return -c;
}
int PartitionVec (int left, int right,
Platform::Collections::Vector<T^>^ vec)
{
int i,j;
i = left;
for (int j = left + 1; j <= right; ++j)
{
if (compare (vec->GetAt(j),vec->GetAt(left)) > 0)
{
++i;
swap (vec,i,j);
}
}
swap (vec,left,i);
return i;
}
void QuickSortVec (Platform::Collections::Vector<T^>^ vec,
int start, int end)
{
if (end > start)
{
int pivot_point;
pivot_point = PartitionVec (start, end, vec);
QuickSortVec (vec,start,pivot_point - 1);
QuickSortVec (vec, pivot_point + 1, end);
}
}