Help needed for writing an algorithm

Here is the description of the the problem

Given an integer N, write a function which returns an integer array of size N, containing the numbers from 1 to N in a random order. Each number from 1 to N must appear once and must not repeat.

• What is the running time of your algorithm?
• Can your algorithm be improved?

For exa开发者_运维技巧mple: if you are given the number 4, your output must generate something like 4213, 2413, 3124, etc.

Invalid outputs would be 1123, 4444, 244.

Any ideas to solve the problem?

Yes it's home work. I just finished writing the algorithm in java, but using Fisher-Yates shuffle seems to be much more efficient. Thank you people. Below is my version of the algorithm.

Collection<Integer> generateNumbers(int n) {
    Collection<Integer> numbers = new HashSet<Integer>();
    Random rand = new Random();
    int max = 0;        
    int min = 0;
    for(int i=0;i<n;i++){
        max=(max*10)+n;
        min=(min*10)+1;
    }
    while(numbers.size()<n){
        int random = rand.nextInt(max-min+1)+min;
        int temp = random;
        boolean good = true;
        Set<Integer> digits = new HashSet<Integer>();
        while(temp>0 && good){
            int reminder = temp%10;
            if(reminder > 0 && reminder <= n ){ 
                digits.add(reminder);
            }else
                good = false;
            temp/=10;
        }       
        if(good && digits.size() == n)
        numbers.add(random);
    }       
    return numbers;
}

Here is a hint: look up what a Fisher-Yates shuffle is.

What you're doing is shuffling an integer array.

Here's an explanation of the Knuth shuffle.