# random pick with weight

🏠
 1from random import randrange
2from itertools import accumulate
3
4class Solution:
5
6    def __init__(self, w):
7        self.w = w
8        self.s = sum(self.w)
9        acc = accumulate(self.w)
10        self.enum = []
11        enum = [*enumerate(acc)]
12        for i, a in enum:
13            l = enum[i - 1][1] if i > 0 else 0
14            u = a if i > 0 else self.w[0]
15            self.enum.append((l, u, i))
16
17    def pickIndex(self) -> int:
18        rand = randrange(0, self.s)
19        l, r = 0, len(self.enum)-1
20        e = self.enum
21        while l <= r:
22            m = (l + r) // 2
23            if e[m][0] <= rand < e[m][1]:
24                return e[m][2]
25            elif rand >= e[m][1]:
26                l = m+1
27            else:
28                r = m-1
29        return e[m][0]
30
31from collections import Counter
32obj = Solution([2, 3])
33counter = Counter()
34
35for i in range(int(1e4)):
36    param_1 = obj.pickIndex()
37    counter[param_1] += 1
38
39print(counter)