Package g0501_0600.s0528_random_pick_with_weight

Class Solution

  • public class Solution
extends Object
    528 - Random Pick with Weight.

    Medium

    You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index.

    You need to implement the function pickIndex(), which randomly picks an index in the range [0, w.length - 1] ( inclusive ) and returns it. The probability of picking an index i is w[i] / sum(w).

    • For example, if w = [1, 3], the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e., 25%), and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e., 75%).

    Example 1:

    Input [“Solution”,“pickIndex”] [1,[]]

    Output: [null,0]

    Explanation:

     Solution solution = new Solution([1]); 
 solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.

    Example 2:

    Input

     ["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
 [[[1,3]],[],[],[],[],[]]

    Output: [null,1,1,1,1,0]

    Explanation:

     Solution solution = new Solution([1, 3]); 
 solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. 
 solution.pickIndex(); // return 1 
 solution.pickIndex(); // return 1 
 solution.pickIndex(); // return 1 
 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. 

 Since this is a randomization problem, multiple answers are allowed. 
 All of the following outputs can be considered correct: 
 [null,1,1,1,1,0] 
 [null,1,1,1,1,1] 
 [null,1,1,1,0,0] 
 [null,1,1,1,0,1] 
 [null,1,0,1,0,0] 
 ...... 
 and so on.

    Constraints:

    • 1 <= w.length <= 104
    • 1 <= w[i] <= 105
    • pickIndex will be called at most 104 times.

    • Constructor Detail

      • Solution

        public Solution​(int[] w)

    • Method Detail

      • pickIndex

        public int pickIndex()