Weighted Random Index Picker Implementation

meta Given an array of positive integers w where w[i] describes the weight of i-th object, implement a function pickIndex which randomly picks an index i from w with that probability proportional to its weight. Implement function: Solution(int[] w): Initialize the object and store the array in it. int pickIndex(): Return a random index, the probability of choosing index i is proportional to w[i]. Maximum input size: The length of w does not exceed 10^4 and the weight does not exceed 10^5. Example Input [1, 3]