《社交网络》里的评分公式——ELO排名系统

　　《社交网络》里的Mark Zackburg被女朋友甩后，在舍友的启发下，充分发挥了技术宅男自娱自乐的恶搞天分，做出了Facemash网站，对学校女生的相貌进行排名打分，结果网站访问流量过大，直接把学校网络搞瘫痪了。Facemask大受欢迎的关键就在于Zackburg基友Eduardo写在窗户上的排名公式，看电影之时就对这个排名公式非常感兴趣，上网了解下，才发现这条公式就是大名鼎鼎的ELO等级分制度。ELO的应用非常广泛，大部分棋类比赛，现在流行的Moba游戏，像11平台的DOTA天梯系统，都是采用ELO等级分。

　　以后做竞技类的游戏排行榜可以用ELO来排名，更真实地反映玩家的实力。闲来无事，做了个flash的Facemask，挺有意思的。

ELO的实现代码

package
{
    
    /**
     * Elo排名算法
     * @author ShuchangLiu
     */
    public class EloRating
    {
        public static const ELO_RESULT_WIN:int = 1;
        public static const ELO_RESULT_LOSS:int = -1;
        public static const ELO_RESULT_TIE:int = 0;
        
        public static const ELO_RATING_DEFAULT:int = 1500;
        
        protected var rating1:int;
        protected var rating2:int;
        protected var score1:Number;
        protected var score2:Number;
        
        public function EloRating(rating1:int = ELO_RATING_DEFAULT, rating2:int = ELO_RATING_DEFAULT):void
        {
            this.rating1 = rating1;
            this.rating2 = rating2;
        }
        
        /**
         * @param result ELO_RESULT_WIN or ELO_RESULT_LOSS or ELO_RESULT_TIE
         */        
        public function setResult(result:int):void {
            var cscore1:Number = computeScore(this.rating2, this.rating1);
            var cscore2:Number = computeScore(this.rating1, this.rating2);
            
            if (result == ELO_RESULT_WIN) {
                this.rating1 = this.rating1 + (computeK(this.rating1) * (1 - cscore1));
                this.rating2 = this.rating2 + (computeK(this.rating2) * (0 - cscore2));
            }else if(result == ELO_RESULT_LOSS) {
                this.rating1 = this.rating1 + (computeK(this.rating1) * (0 - cscore1));
                this.rating2 = this.rating2 + (computeK(this.rating2) * (1 - cscore2));
            }else{
                // Assume tie
                this.rating1 = this.rating1 + (computeK(this.rating1) * (0.5 - cscore1));
                this.rating2 = this.rating2 + (computeK(this.rating2) * (0.5 - cscore2));
            }
        }
        
        protected function computeScore($rating1:int, $rating2:int):Number {
            return (1 / (1 + Math.pow(10, ($rating1 - $rating2) / 400)));
        }
        
        protected function computeK(rating:int):int {
            if(rating>=2400){
                return 16;
            }else if(rating >= 2100){
                return 24;
            }else{
                return 36;
            }
        }
        
        /** A的获胜期望*/
        public function getScore1():Number {
            this.score1 = computeScore(this.rating2, this.rating1);
            return this.score1;
        }
        
        /** B的获胜期望*/
        public function getScore2():Number {
            this.score2 = computeScore(this.rating1, this.rating2);
            return this.score2;
        }
        
        /** A的排名等级*/
        public function getRating1():int {
            return this.rating1;
        }
        
        /** B的排名等级*/
        public function getRating2():int {
            return this.rating2;
        }
        
        
        
    }
}