Aho-Corasick算法实现（简单关键字过滤）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleAppTest
{
    class Program
    {
        /// <summary>
        /// 简单关键字过滤
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            var ss = CheckDirtyWords("sswo1lfsss殺殺殺喫屎阿三大蘇打阿薩大大愛的愛的大量加拉傑拉德拉薩大家安靜杜拉斯的就拉客的就拉省的家裏卡等級了及案例記錄記錄加拉多久啦結束了");
            Console.WriteLine(ss);
            Console.ReadLine();
        }

        /// <summary>
        /// 检查指定的内容是否包含非法关键字
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        protected static bool CheckDirtyWords(string text)
        {
            var dirtyStr = "wolf|jason|hoho|barry|喫屎";
            if (string.IsNullOrEmpty(dirtyStr))
            {
                return false;
            }
            List<string> keywords = dirtyStr.Split('|').ToList();
            KeywordFilter ks = new KeywordFilter(keywords);
            return ks.FindAllKeywords(text).Count > 0;
        }
    }


    /// <summary>
    /// Aho-Corasick算法实现
    /// </summary>
    public class KeywordFilter
    {
        /// <summary>
        /// 构造节点
        /// </summary>
        private class Node
        {
            private Dictionary<char, Node> transDict;

            public Node(char c, Node parent)
            {
                this.Char = c;
                this.Parent = parent;
                this.Transitions = new List<Node>();
                this.Results = new List<string>();

                this.transDict = new Dictionary<char, Node>();
            }

            public char Char
            {
                get;
                private set;
            }

            public Node Parent
            {
                get;
                private set;
            }

            public Node Failure
            {
                get;
                set;
            }

            public List<Node> Transitions
            {
                get;
                private set;
            }

            public List<string> Results
            {
                get;
                private set;
            }

            public void AddResult(string result)
            {
                if (!Results.Contains(result))
                {
                    Results.Add(result);
                }
            }

            public void AddTransition(Node node)
            {
                this.transDict.Add(node.Char, node);
                this.Transitions = this.transDict.Values.ToList();
            }

            public Node GetTransition(char c)
            {
                Node node;
                if (this.transDict.TryGetValue(c, out node))
                {
                    return node;
                }

                return null;
            }

            public bool ContainsTransition(char c)
            {
                return GetTransition(c) != null;
            }
        }

        private Node root; // 根节点
        private string[] keywords; // 所有关键词

        public KeywordFilter(IEnumerable<string> keywords)
        {
            this.keywords = keywords.ToArray();
            this.Initialize();
        }

        /// <summary>
        /// 根据关键词来初始化所有节点
        /// </summary>
        private void Initialize()
        {
            this.root = new Node(' ', null);

            // 添加模式
            foreach (string k in this.keywords)
            {
                Node n = this.root;
                foreach (char c in k)
                {
                    Node temp = null;
                    foreach (Node tnode in n.Transitions)
                    {
                        if (tnode.Char == c)
                        {
                            temp = tnode; break;
                        }
                    }

                    if (temp == null)
                    {
                        temp = new Node(c, n);
                        n.AddTransition(temp);
                    }
                    n = temp;
                }
                n.AddResult(k);
            }

            // 第一层失败指向根节点
            List<Node> nodes = new List<Node>();
            foreach (Node node in this.root.Transitions)
            {
                // 失败指向root
                node.Failure = this.root;
                foreach (Node trans in node.Transitions)
                {
                    nodes.Add(trans);
                }
            }
            // 其它节点 BFS
            while (nodes.Count != 0)
            {
                List<Node> newNodes = new List<Node>();
                foreach (Node nd in nodes)
                {
                    Node r = nd.Parent.Failure;
                    char c = nd.Char;

                    while (r != null && !r.ContainsTransition(c))
                    {
                        r = r.Failure;
                    }

                    if (r == null)
                    {
                        // 失败指向root
                        nd.Failure = this.root;
                    }
                    else
                    {
                        nd.Failure = r.GetTransition(c);
                        foreach (string result in nd.Failure.Results)
                        {
                            nd.AddResult(result);
                        }
                    }

                    foreach (Node child in nd.Transitions)
                    {
                        newNodes.Add(child);
                    }
                }
                nodes = newNodes;
            }
            // 根节点的失败指向自己
            this.root.Failure = this.root;
        }

        /// <summary>
        /// 找出所有出现过的关键词
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public List<KeywordSearchResult> FindAllKeywords(string text)
        {
            List<KeywordSearchResult> list = new List<KeywordSearchResult>();

            Node current = this.root;
            for (int index = 0; index < text.Length; ++index)
            {
                Node trans;
                do
                {
                    trans = current.GetTransition(text[index]);

                    if (current == this.root)
                        break;

                    if (trans == null)
                    {
                        current = current.Failure;
                    }
                } while (trans == null);

                if (trans != null)
                {
                    current = trans;
                }

                foreach (string s in current.Results)
                {
                    list.Add(new KeywordSearchResult(index - s.Length + 1, s));
                }
            }

            return list;
        }

        /// <summary>
        /// 简单地过虑关键词
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public string FilterKeywords(string text)
        {
            StringBuilder sb = new StringBuilder();

            Node current = this.root;
            for (int index = 0; index < text.Length; index++)
            {
                Node trans;
                do
                {
                    trans = current.GetTransition(text[index]);

                    if (current == this.root)
                        break;

                    if (trans == null)
                    {
                        current = current.Failure;
                    }

                } while (trans == null);

                if (trans != null)
                {
                    current = trans;
                }

                // 处理字符
                if (current.Results.Count > 0)
                {
                    string first = current.Results[0];
                    sb.Remove(sb.Length - first.Length + 1, first.Length - 1);// 把匹配到的替换为**
                    sb.Append(new string('*', current.Results[0].Length));

                }
                else
                {
                    sb.Append(text[index]);
                }
            }

            return sb.ToString();
        }
    }

    /// <summary>
    /// 表示一个查找结果
    /// </summary>
    public struct KeywordSearchResult
    {
        private int index;
        private string keyword;
        public static readonly KeywordSearchResult Empty = new KeywordSearchResult(-1, string.Empty);

        public KeywordSearchResult(int index, string keyword)
        {
            this.index = index;
            this.keyword = keyword;
        }

        /// <summary>
        /// 位置
        /// </summary>
        public int Index
        {
            get { return index; }
        }

        /// <summary>
        /// 关键词
        /// </summary>
        public string Keyword
        {
            get { return keyword; }
        }
    }
}