游戏 掉落算法

1、前言
在游戏开发中很多功能按权重随机给东西，比如：掉落、奖励、抽奖等等.....

2、功能

*）支持多个权重进行随机

*）能屏蔽指定权重，防止再次随机到

3、实现

 public int weightRandom(BitSet exclude, int... weights) {
         if (weights == null) {
             //安全性验证
         }
         int length = weights.length;
         if (length == 0) {
             return -1;
         }

         if (len == 1) {
             int w = weights[0];
             if (w < 0) {
                 //安全性验证
             } else if (w == 0) {
                 return -1;
             } else {
                 return 0;
             }
         }

         int total = 0;
         for (int i = 0; i < len; i++) {
             if (exclude != null && exclude.get(i)) {
                 continue;
             }
             int w = weights[i];
             total += w;
         }
         if (total <= 0) {
             return -1;
         }
         int randomNum = random(1, total), hitIndex = -1, partNum = 0;
         for (int i = 0; i < len; i++) {
             if (exclude != null && exclude.get(i)) {
                 continue;
             }
             int w = weights[i];
             partNum += w;
             if (partNum >= randomNum) {
                 hitIndex = i;
                 break;
             }
         }
         return hitIndex;
 }