字符串相似度算法，AS3实现，用于判断聊天广告

        /**
         * 计算把source经过几个步骤可以转变到target的值 
         * @param source
         * @param target
         * @return 
         * 
         */
        public static function editDistance(source:String,target:String):int
        {
            var slen:int = source.length;
            var tlen:int = target.length;
            var d:Array = [];
            for(var i:int=0;i<=slen;i++){
                d[i] = [];
                d[i][0] = i;
                if(i==0){
                    for(var j:int=1;j<=tlen;j++){
                        d[0][j] = j;
                    }
                }
                else
                {
                    for(var j:int=1;j<=tlen;j++){
                        d[i][j] = 0;
                    }
                }
            }
            for(var i:int=1;i<=slen;i++){
                for(var j:int=1;j<=tlen;j++){
                    if(source.charCodeAt(i-1) == target.charCodeAt(j-1)){
                        d[i][j] = d[i-1][j-1];
                    } else {
                        var insert:int = d[i][j-1]+1;
                        var del:int = d[i-1][j]+1;
                        var update:int = d[i-1][j-1]+1;
                        d[i][j] = Math.min(insert,del)>Math.min(del,update)?
                            Math.min(del,update):Math.min(insert,del);
                    }
                }
            }
            return d[slen][tlen];
        }
        
        /**
         * 相似度计算 
         * @param source
         * @param target
         * @return 
         * 
         */
        public static function getSimilarityRate(source:String,target:String):Number
        {
            return 1-editDistance(source,target)/Math.max(source.length,target.length);
        }