Hi guys :),
I have a problem with Shuffling this array:
int questionNumberArray[10]={0,1,2,3,4,5,6,7,8,9};
does anyone know a build in function or a way to shuffle the values in the array without any repeating?
Well I myself would Google for:
shuffle algorithm
What I usually do is swap each entry with a random other entry:
int questionNumberArray[]={0,1,2,3,4,5,6,7,8,9};
const int questionCount = sizeof questionNumberArray / sizeof questionNumberArray[0];
for (int i=0; i < questionCount; i++) {
int n = random(0, questionCount); // Integer from 0 to questionCount-1
int temp = questionNumberArray[n];
questionNumberArray[n] = questionNumberArray[i];
questionNumberArray[i] = temp;
}
@John: I'd feel a little better if n were a long rather than an int.
Homework question.
How would you shuffle ianything?
@PaulMurrayCbr: This is the Google code mentioned earlier with a few minor modifications.
void setup() {
int i;
Serial.begin(9600);
int arr[] = {0, 1, 2, 3, 4, 5, 6, 7, 8};
int n = sizeof(arr)/ sizeof(arr[0]);
randomize (arr, n);
for (i - 0; i < n; i++) {
Serial.print(arr[i]);
Serial.print(" ");
}
}
void loop() {
}
void swap (int *a, int *b)
{
int temp = *a;
*a = *b;
*b = temp;
}
void randomize ( int arr[], int n )
{
// Use a different seed value so that we don't get same
// result each time we run this program
randomSeed(analogRead(A0));
// Start from the last element and swap one by one. We don't
// need to run for the first element that's why i > 0
for (int i = n-1; i > 0; i--)
{
long j = random(0, n);
swap(&arr[i], &arr[j]);
}
}
If you mean how can you shuffle any type of data, all you need to do it alter the swap() function. You could even pre-write swap routines for the basic data types and call via a pointer to function if the data type is determined at run time.
PaulMurrayCbr:
Homework question.How would you shuffle ianything?
gynintahi
econjack:
@John: I'd feel a little better if n were a long rather than an int.
Why? The value is constrained to be within 0 and the length of the array....
Regards,
Ray L.
A slightly faster algorithm which optimizes the swap, useful mainly (only) for large array's or on external devices. In memory the costs of random() far outweighs almost any optimization. Using a faster random makes more sense.
void shuffleArray(int * array, int size)
{
int last = 0;
int temp = array[last];
for (int i=0; i<size; i++)
{
int index = random(size);
array[last] = array[index];
last = index;
}
array[last] = temp;
}