Last updated on July 18th, 2024 at 03:43 am

Here, We see Random Pick Index LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

List of all LeetCode Solution

Topics

Reservoir Sampling

Companies

Facebook

Level of Question

Medium

Random Pick Index LeetCode Solution

Problem Statement

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.

1. Random Pick Index LeetCode Solution C++

class Solution {
public:
    unordered_map<int,vector<int>> m;
    Solution(vector<int>& nums) {
        for(int i=0;i<nums.size();i++)
        {
            m[nums[i]].push_back(i);
        }
    }
    int pick(int target) {
        int x=m[target].size();
        x=rand()%x;
        return m[target][x];
    }
};

2. Random Pick Index LeetCode Solution Java

class Solution {
    int[] nums;
    Random random;
    public Solution(int[] nums) {
        this.nums = nums;
        this.random = new Random();
    }
    public int pick(int target) {
        int idx = -1;
        int count = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == target) {
                count++;
                if (random.nextInt(count) == 0) {
                    idx = i;
                }
            }
        }
        return idx;
    }
}

3. Random Pick Index Solution JavaScript

var Solution = function(nums) {
    this.nums = nums;
    this.len = nums.length;
};
Solution.prototype.pick = function(target) {
    if (this.len == 1) return 0;
    var result = 0;
    var count = 0;
    for (var i = 0; i < this.len; i++) {
        if (this.nums[i] == target) {
            if (Math.floor(Math.random() * (++count)) == 0) result = i;
        }
    }
    return result;
};

4. Random Pick Index Solution Python

class Solution(object):
    def __init__(self, nums):
        self.indices = defaultdict(list)
        for i, num in enumerate(nums):
            self.indices[num].append(i)
    def pick(self, target):
        return random.choice(self.indices[target])