List.cs

// As we all know, the generic List<T> class in .NET doesn't 
// have a RemoveMultiple method. Could you implement it for me?
// Say the elements are kept in the _items field, which is an
// array of type T. Also, use _count to keep the current number
// of elements.
// PS: You can compare two items with "==" operator.

namespace System.Collections.Generic
{
    public class List<T>
    {
        private T[] _items;
        private int _count;
        
        public void RemoveMultiple(IEnumerable<T> itemsToRemove)
        {
            // Please implement the method here.
        }
    }
}

void Main()
{
    var list = new List<int>(new[] {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 });
    var itemsToRemove = new int[] {0, 1, 2, 3, 4, 5, 6, 7, 8, };
    list.Print();
    list.RemoveMultiple(itemsToRemove);
    list.Print();
}

// Define other methods and classes here
    public class List<T>
    {
        private T[] _items;
        private int _count;

        public List(IEnumerable<T> values)
        {
            _items = values.ToArray();
            _count = _items.Length;
        }

        public void Print()
        {
            Console.WriteLine(string.Join(", ", _items.Take(_count).Select(x => x.ToString())));
        }


        public void RemoveMultiple(IEnumerable<T> itemsToRemove)
        {
            // Please implement the method here.
            // == 无法通过编译, 这里用了 object.Equals
            // 如果查找时间过长,并且可以排序,可以合并算法更快找出所有要删除的索引位置, 此处从略
            var indeces = _items.Select((item, index) => new {item, index})
                .Where(x => itemsToRemove.Any(y => Equals(y, x.item)))
                .Select(x => x.index)
                .OrderBy(x => x)
                .ToList();

            for(var i = 0; i < indeces.Count; i++)
            {
                var indexStart = indeces[i] - i;
                var indexEnd = (i < indeces.Count - 1 ? indeces[i+1] : _count -1) -i;

                for(var index = indexStart; index < indexEnd; index++)
                {
                    _items[index] = _items[index+i+1];
                }
            }
            _count = _count - indeces.Count;
        }
    }

睡一半想到昨天写错了。。。

    public void RemoveMultiple(IEnumerable<T> itemsToRemove)
    {
        foreach (T item in itemsToRemove)
        {
            for (int i = 0; i < _count; i++)
            {
                if (_items[i] == item)
                {
                    _items[i] = null;
                    break;
                }
            }
        }

        int p = 0;
        int q = 0;

        while( p != _count )
        {
            if (!_items[p] == null)
            {
                if (p != q)
                {
                    _items[q] = _items[p];  
                }

                q++;
            }

            p++;
        }

        for (int i = q; i < _count; i++)
        {
            _items[i] = null;
        }

        _count = q;
    }