过滤或筛出数组中的重复项

int[] list = new int[] { 1, 2, 3, 4, 5, 4, 4, 2, 6, 8, 9 };
// 非重复项  
var distincts = list.Distinct();
// 重复项  
var duplicates = list.GroupBy(i => i)
                        .Where(g => g.Count() > 1)
                        .Select(o => o.Key);