如何在c ++中混合使用n个值的数组

Question

I'm trying to make a function that mixes up the values of a given ordered array, say from 0 to n. So this is my try:

void JumbleUp(int *sorted,int n){
int jumble[n];
bool mark[n];
for(int i=0;i<n;i++)
    mark[i]=false;
int aux=0;
srand(time(NULL));
for(int i=0;i<n;i++){

    do {
        aux=(rand()%n);
        }while (mark[aux]);

    jumble[i]=sorted[aux];
    mark[aux]=true;
    }

The problem is that this function doesn't work for big integers because it takes a lot of time. So what can I do to improve my function or what others alternatives can I use to jumble up an array.

Answer 1

You are overthinking it. First of all call srand only once when program starts. Then for algorithm, something like pseudocode

for index in 0..n-1
    index2 = random (0..n-1)
    swap (ar, index, index2)

I could be wrong here, but I think it's important to get index2 in above range 0..n-1 and not for example index..n-1 , so every piece has equal chance to end up in all locations. Alternative suggested in comment is this, which may also produce evenly distributed shuffle:

for index in 0..n-2
    index2 = random (index..n-1)
    swap (ar, index, index2)