Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array.
Note:
The array size can be very large. Solution that uses too much extra space will not pass the judge.
Example:
int[] nums = new int[] {1,2,3,3,3};
Solution solution = new Solution(nums);
// pick(3) should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
solution.pick(3);
// pick(1) should return 0. Since in the array only nums[0] is equal to 1.
solution.pick(1);
my solution is memory limit exceeded
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12import random
import collections
class Solution(object):
def __init__(self, nums):
self.nums = nums
def pick(self, target):
index_dict = collections.defaultdict(list)
for i,n in enumerate(self.nums):
index_dict[n].append(i)
return random.choice(index_dict[target])Reservoir Sampling solution
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17import random
import collections
class Solution(object):
def __init__(self, nums):
self.nums = nums
def pick(self, target):
count, index = 0, 0
for i, n in enumerate(self.nums):
if n == target:
count += 1
rand = random.randint(1, count)
if rand == count:
index = i
return index