在给定的一个大数列中，随机抽出一个子数列，要求所有数被抽出的概率都是一样的，如下面的运行结果：

int rangeRandNum(int a, int b)
{
	return rand()%(b-a+1) + a;
}


vector<int> randPickArray(vector<int> &arr, int m)
{
	vector<int> picks(arr.begin(), arr.begin()+m);
	for (int i = m; i < arr.size(); i++)
	{
		int t = rangeRandNum(0, i);
		if (t < m)
		{
			picks[t] = arr[i];
		}
	}
	return picks;
}


int main() 
{
	int tar = 7;
	int cand[] = {1,2,3,0,3,2,0,3,1,4,5,3,2,7,5,3,0,1,2,1,3,4,6,8,1,8};

	srand(time(time_t(NULL)));

	vector<int> v(cand, cand+sizeof(cand)/sizeof(int));
	for (auto x:v)
		cout<<x<<" ";
	cout<<endl;

	vector<int> r = randPickArray(v, 6);

	for (auto x:r)
		cout<<x<<" ";
	cout<<endl;

	system("pause"); 
	return 0;
}

Craking the Coding Interview 面试题：随机抽出子数列