带权随机在游戏开发中重度使用,各种抽奖和爆装备等.

运营根据需要来配置各个物品出现的概率.

今天要说的这个带权随机算法思想很简单,就是"把所有物品根据其权重构成一个个区间,权重大的区间大.可以想象成一个饼图.  然后,扔骰子,看落在哪个区间,"

举个栗子,有个年终抽奖,物品是iphone/ipad/itouch.

主办方配置的权重是[(‘iphone‘, 10), (‘ipad‘, 40), (‘itouch‘, 50)].

用一行代码即可说明其思想,即random.choice([‘iphone‘]*10 + [‘ipad‘]*40 + [‘itouch‘]*50).

下面,我们写成一个通用函数.

#coding=utf-8
import random
def weighted_random(items):
    total = sum(w for _,w in items)
    n = random.uniform(0, total)#在饼图扔骰子
    for x, w in items:#遍历找出骰子所在的区间
        if n<w:
            break
        n -= w
    return x

print weighted_random([('iphone', 10), ('ipad', 40), ('itouch', 50)])

物品越多,二分查找提升的性能越明显.

#coding=utf-8
class WeightRandom:
    def __init__(self, items):
        weights = [w for _,w in items]
        self.goods = [x for x,_ in items]
        self.total = sum(weights)
        self.acc = list(self.accumulate(weights))

    def accumulate(self, weights):#累和.如accumulate([10,40,50])->[10,50,100]
        cur = 0
        for w in weights:
            cur = cur+w
            yield cur

    def __call__(self):
        return self.goods[bisect.bisect_right(self.acc , random.uniform(0, self.total))]

wr = WeightRandom([('iphone', 10), ('ipad', 40), ('itouch', 50)])
print wr()

飘逸的python - 带权随机算法及在抽奖中的应用