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Java-based LeetCode algorithm problem solutions, regularly updated
398\. Random Pick Index
Medium
Given an integer array `nums` 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.
Implement the `Solution` class:
* `Solution(int[] nums)` Initializes the object with the array `nums`.
* `int pick(int target)` Picks a random index `i` from `nums` where `nums[i] == target`. If there are multiple valid i's, then each index should have an equal probability of returning.
**Example 1:**
**Input**
["Solution", "pick", "pick", "pick"]
[[[1, 2, 3, 3, 3]], [3], [1], [3]]
**Output:** [null, 4, 0, 2]
**Explanation:**
Solution solution = new Solution([1, 2, 3, 3, 3]);
solution.pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
solution.pick(1); // It should return 0. Since in the array only nums[0] is equal to 1.
solution.pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
**Constraints:**
* 1 <= nums.length <= 2 * 104
* -231 <= nums[i] <= 231 - 1
* `target` is an integer from `nums`.
* At most 104 calls will be made to `pick`.