高效率随机删除数据（不重复）

算法的复杂度就降低为 O(n) ，速度大大提高。

需求：前后数据x条不动，中间随机删除N条记录

实现：

 Dictionary<string, int> dictA = GetArrayListFromTxt(this.txtFileNameA.Text);
Dictionary<string, int> dictB = GetArrayListFromTxt(this.txtFileNameB.Text);
Dictionary<string, int> dictC= new Dictionary<string,int>();
StringBuilder sb=new StringBuilder();
foreach (var item in dictB)
{
if (dictA.ContainsKey(item.Key))
{
dictA.Remove(item.Key);
dictC.Add(item.Key, item.Value);
sb.AppendLine(item.Key);
}
}
textBox1.Text = sb.ToString();
txtRepeatNum.Text = Convert.ToString(dictC.Count );
foreach (object key in RandomValues(dictA,x).Take(n))
{
dictA.Remove(key.ToString());
}

算法：

 public static IEnumerable<TKey> RandomValues<TKey, TValue>(IDictionary<TKey, TValue> dict,int num)
{
List<TKey> list = Enumerable.ToList( dict.Select(k=>k.Key).Skip(Convert.ToInt32(num)).Take(dict.Count - num * 2));
Random rand = new Random();
while (list.Count > 0)
{
var point = rand.Next(0, list.Count);
var rv = list[point];
list[point] = list[list.Count - 1];
list.RemoveAt(list.Count - 1);
yield return rv;
}
}