How would I go about determining if a number is a multiple of 5?
In my app, I want one method to run if a certain number is not a multiple of 5, and another method to run if the method is a multiple of 5.
Thanks for your help!
Swift 5 UPDATE
According to newly released language version you can determine this using isMultiple(of:) method
let num = 75
if num.isMultiple(of: 5) {
// multiple of 5
} else {
// not a multiple of 5
}
Use the modulus operator to check the remainder of integer division.
if (num % 5 == 0) {
// multiple of 5.
}
else {
// not a multiple of 5.
}
Use the modulus operator:
if (num % 5 == 0)
//the number is a multiple of 5.
else
// the number is not a multiple of 5.
The modulus operator returns the remainder of a division instead of the division itself, so this logic will work with any number, not just 5. i.e. if (num % 3 == 0) //multiple of 3
Check by this simple logic.
Find the remainder, if it is 0, that means it is completely divisible by 5.
if(number % 5 == 0) {
NSLog(#"Multiple of 5");
//[self multipleOfFive];//your method
}
else{
NSLog(#"Not a multiple of 5");
//[self notMultipleOfFive];//your method
}
Note: You can only check % (modulus) for integers
for floats or doubles use :
double fmod(double x, double y);
float fmodf(float x, float y);
long double fmodl(long double x, long double y);
Related
Could someone explain to me the logic behind this hashMap algorithm? I'm getting confused about how the algorithm receives the total sum. I'm starting to learn about algorithms, so it's a little confusing for me. I made comments in my code to pinpoint each line code, but I'm not sure I'm grasping logic correctly. I'm just looking for an easier way to understand how the algorithm works to avoid confusing myself.
//**calculate Two Number Sum
func twoNumberSum(_ array: [Int], _ targetSum: Int) -> [Int] {
//1) initilize our Array to hold Integer Value: Boolean value to store value into hashTable
var numbersHashMap = [Int:Bool]()
//2) create placeHolder called number that iterates through our Array.
for number in array {
//3) variable = y - x
let match = targetSum - number
//4) ??
if let exists = numbersHashMap[match], exists {
//5) match = y / number = x
return [match, number] //
} else {
//6) Store number in HashTable and repeats
numbersHashMap[number] = true
}
}
return []
}
twoNumberSum([3,5,-4, 8, 11, 1, -1, -6], 10)
// x = Number
// y = Unknown *Solve for Y*
Sure, I can walk you through it. So we have a list of numbers, are we are trying to find two numbers that add together to make the specified target. To do this, for each number x, we check if (target - x) is in the list. If it is not, then we add x to the list. If it is, then we return x and (target - x).
Step 4 in your code is the part where we check if (target - x) is in the list. To see why this makes sense, let's walk through an example.
Say we have [2, 3, -1] and our target is 1. In this case, we first consider x = 2 and check our hashmap for (target - x) = (1 - 2) = -1. Since -1 is not in the hashmap, we add 2 to the hashmap. We then consider x = 3 and check for (1 - 3) = -2. Again, -2 is not in the hashmap, so we add it. Now we check x - -1. In this case, when we check (target - x) = (1 - (-1)) = 2, 2 is in the hashmap. Intuitively, we have already "seen" 2, and know that 2 and -1 can be added to get our value.
This is what provides the speed optimization over checking every two numbers in the list.
I have an app with a 6x7 grid that lets the user input values. After each value is obtained the app checks to find if any of the consecutive values create a sum of ten and executes further code (which I have working well for the 4 test cases I've written). So far I've been writing if statements similar to the below:
func findTens() {
if (rowOneColumnOnePlaceHolderValue + rowOneColumnTwoPlaceHolderValue) == 10 {
//code to execute
} else if (rowOneColumnOnePlaceHolderValue + rowOneColumnTwoPlaceHolderValue + rowOneColumnThreePlaceHolderValue) == 10 {
//code to execute
} else if (rowOneColumnOnePlaceHolderValue + rowOneColumnTwoPlaceHolderValue + rowOneColumnThreePlaceHolderValue + rowOneColumnFourPlaceHolderValue) == 10 {
//code to execute
} else if (rowOneColumnOnePlaceHolderValue + rowOneColumnTwoPlaceHolderValue + rowOneColumnThreePlaceHolderValue + rowOneColumnFourPlaceHolderValue + rowOneColumnFivePlaceHolderValue) == 10 {
//code to execute
}
That's not quite halfway through row one, and it will end up being a very large set of if statements (231 if I'm calculating correctly, since a single 7 column row would be 1,2-1,2,3-...-2,3-2,3,4-...-67 so 21 possibilities per row). I think there must be a more concise way of doing it but I've struggled to find something better.
I've thought about using an array of each of the rowXColumnYPlaceHolderValue variables similar to the below:
let rowOnePlaceHolderArray = [rowOneColumnOnePlaceHolderValue, rowOneColumnTwoPlaceHolderValue, rowOneColumnThreePlaceHolderValue, rowOneColumnFourPlaceHolderValue, rowOneColumnFivePlaceHolderValue, rowOneColumnSixPlaceHolderValue, rowOneColumnSevenPlaceHolderValue]
for row in rowOnePlaceHolderArray {
//compare each element of the array here, 126 comparisons
}
But I'm struggling to find a next step to that approach, in addition to the fact that those array elements then apparently because copies and not references to the original array anymore...
I've been lucky enough to find some fairly clever solutions to some of the other issues I've come across for the app, but this one has given me trouble for about a week now so I wanted to ask for help to see what ideas I might be missing. It's possible that there will not be another approach that is significantly better than the 231 if statement approach, which will be ok. Thank you in advance!
Here's an idea (off the top of my head; I have not bothered to optimize). I'll assume that your goal is:
Given an array of Int, find the first consecutive elements that sum to a given Int total.
Your use of "10" as a target total is just a special case of that.
So I'll look for consecutive elements that sum to a given total, and if I find them, I'll return their range within the original array. If I don't find any, I'll return nil.
Here we go:
extension Array where Element == Int {
func rangeOfSum(_ sum: Int) -> Range<Int>? {
newstart:
for start in 0..<count-1 {
let slice = dropFirst(start)
for n in 2...slice.count {
let total = slice.prefix(n).reduce(0,+)
if total == sum {
return start..<(start+n)
}
if total > sum {
continue newstart
}
if n == slice.count && total < sum {
return nil
}
}
}
return nil
}
}
Examples:
[1, 8, 6, 2, 8, 4].rangeOfSum(10) // 3..<5, i.e. 2,8
[1, 8, 1, 2, 8, 4].rangeOfSum(10) // 0..<3, i.e. 1,8,1
[1, 8, 3, 2, 9, 4].rangeOfSum(10) // nil
Okay, so now that we've got that, extracting each possible row or column from the grid (or whatever the purpose of the game is) is left as an exercise for the reader. 🙂
I'm learning an swift and I've written two functions and have tried them on their own they both work well. However when I try to call one function within another one I can't seem to get the desired out-put that I seek.
The task at hand is that one function should print Prime numbers whilst the other is to calculate and check if the number is prime. I am supposed to call the check if number is prime from the print Prime numbers function.
below is my code:
This function calculates whether or not the X:Int is a prime number. It's set to a boolean because I'm supposed to print "true" or "false" in the function below it.
func isPrime(_ x: Int) -> Bool {
if(x%2 == 0 || x%3 == 0){
if(x == 2 || x == 3){
return(true)
}
return(false)
}
else{
//if the number is less than or equal to 1, we'll say it's not prime
if(x <= 1){
return(false)
}
}
return true
}
This piece calculates the printing of the prime number from 1 to n.
func PrintPrimes(upTo n: Int) {
for x in 1...n {
var count = 0
for num in 1..<x {
isPrime(x)
count += 1
}
if count <= 1 {
print(isPrime(x))
}
}
}
This piece only runs twice and i'm not exactly sure why. I don't know if its because i'm not calling it correctly or I'd have to change up some calculations.
All help is appreciated
EDIT:
Here is the original printPrimes() before I decided to call isPrime within the function. This function calculates the prime numbers only and prints them up to n.
func printPrimes(upTo n: Int) {
for x in 1...n {
var count = 0
for num in 1..<x {
if x % num == 0 {
count += 1
}
}
if count <= 1 {
print(x)
}
}
}
Your second routine is printing only two values because it is calling isPrime, but never doing anything conditional on the value returned, but rather incrementing count regardless. And since you’re printing only if count is <= 1, that will happen only for the first two values of n.
But let’s say you were trying to print the prime numbers up to a certain number, you could do:
func printPrimes(upTo n: Int) {
for x in 1...n {
if isPrime(x) {
print(x)
}
}
}
(As a matter of convention, in Swift, when we say “through n”, we’d iterate 1...n, and if someone said “up to n”, we’d iterate 1..<n. But because your original code snippet uses upTo in conjunction with 1...n, I’ll use that here, but just note that this isn’t very consistent with standard Swift API patterns.)
Unfortunately, isPrime is not correct, either. So you’ll have to fix that first. For example, consider 25. That is not divisible by 2 or 3, but isn’t prime, either.
If you look at the original printPrimes that was provided, what it effectively does is say “by how many whole integers less than x is x divisible ... if only divisible by one other number (namely 1), then it’s a prime.” That logic, although not efficient, is correct. You should go ahead and use that inside your isPrime routine. But that “is divisible by 2 or 3” logic is not correct.
You can do it this way, in your printPrimes you can loop up to the number you want and just check if the number is prime by calling the function with the number. But you have to check your isPrime function. Your printPrimes should only do what its name says (print the prime numbers up to n) and all the logic to check if the number is prime should be on your isPrime function.
Also its a good practice to use camelCase on functions, you should rename your function to printPrimes instead of PrintPrimes.
func printPrimes(upTo n: Int) {
for x in 1...n {
if isPrime(x) {
print(x)
}
}
}
I have an array of coordinates (965 in total). I want to use these coordinates in Google Roads API however the limit is 100.
I have a function that determines how many items in the array and then gets the value to use.
round(Double(userCoordinatesHardCoded.count / 100))
produces 9.
I would like to remove ALL items that are not at indexes that are multiples of, in this case, 9. So in theory I will only ever have no more than 100 items in the array.
If possible, I would like to keep the first and last array item.
I know this has already been answered, but this is a great use case for using the filter function built into Swift:
let newCoordinates = oldCoordinates.filter { coord in
return (coord % 9 != 0)
}
If space is not a problem, you can create another array with the desired multiples.
var oldCoordinates // Imagine it having all those elements
var newCoordinates : GoogleCoordinates = [] // This one will have new ones
newCoordinates.append(oldCoordinates[0])
var x = 1
for (x; x < oldCoordinates.count ; x++ ) {
if (x % 5 == 0) {
newCoordinates.append(oldCoordinates[x])
}
}
if (x != (oldCoordinates.count - 1)) {
newCoordinates.append(oldCoordinates[oldCoordinates.count - 1])
}
I think I'm going insane.
"counter" and "interval" are both doubles. This is happening on accelerometer:didAccelerate at an interval of (.01) . "counter" should eventually increment to "interval". For some reason i cant get this "if" to ring true.
Am I overlooking something?
double interval = .5;
if( counter == interval ){ //should eventually be .50000 == .50000
NSLog( #"Hit!" );
[self playSound];
counter = 0;
}else{
counter += .01;
}
NSLog( #"%f, %f, %d",counter,interval,(counter == interval) );
Don't ever compare doubles or floats with equality - they might look the same at the number of significant figures your are examining but the computer sees more.
For this purpose, the Foundation Framework provides "epsilon" values for different types such as "float" and "double". If the distance between two numbers is smaller than epsilon, you can assume these two numbers are equal.
In your case, you would use it as follow:
- (BOOL)firstDouble:(double)first isEqualTo:(double)second {
if(fabs(first - second) < DBL_EPSILON)
return YES;
else
return NO;
}
Or in Swift 4:
func doublesAreEqual(first: Double, second: Double) -> Bool {
if fabs(first - second) < .ulpOfOne {
return true
}
return false
}
Two very useful links:
What Every Computer Scientist Should Know About Floating-Point Arithmetic
Interesting discussion of Unit in Last Place (ULP) and usage in Swift
Friday Q&A 2011-01-04: Practical Floating Point
In your else block, you are not adding 0.01 to counter, because that is not a representable double-precision value. You are actually adding the value:
0.01000000000000000020816681711721685132943093776702880859375
Unsurprisingly, when you repeatedly add this value to itself, you never get 0.5 exactly.
Two options: the better is to replace the if condition with (counter >= interval). Alternatively, you could use a small power of two for the increment instead of something that cannot be represented, like 0.0078125.