> For the complete documentation index, see [llms.txt](https://garylai.gitbook.io/algorithm-and-data-structure/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://garylai.gitbook.io/algorithm-and-data-structure/common-algorithms/reservoir-sampling/random-pick-index.md).

# 398. Random Pick Index

[398. Random Pick Index](https://leetcode.com/problems/random-pick-index/)

```python
class Solution:

    def __init__(self, nums: List[int]):
        self.nums = nums

    def pick(self, target: int) -> int:
        k = 1
        res = None

        for i, n in enumerate(self.nums):
            if n == target:
                if random.random() < 1/k:
                    res = i
                k += 1
        return res



# Your Solution object will be instantiated and called as such:
# obj = Solution(nums)
# param_1 = obj.pick(target)
```