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  • [LC] 528. Random Pick with Weight

    Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight.

    Note:

    1. 1 <= w.length <= 10000
    2. 1 <= w[i] <= 10^5
    3. pickIndex will be called at most 10000 times.

    Example 1:

    Input: 
    ["Solution","pickIndex"]
    [[[1]],[]]
    Output: [null,0]
    

    Example 2:

    Input: 
    ["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
    [[[1,3]],[],[],[],[],[]]
    Output: [null,0,1,1,1,0]

    Explanation of Input Syntax:

    The input is two lists: the subroutines called and their arguments. Solution's constructor has one argument, the array wpickIndex has no arguments. Arguments are always wrapped with a list, even if there aren't any.

    class Solution {
        int[] arr;
        private Random rand;
    
        public Solution(int[] w) {
            arr = new int[w.length];
            arr[0] = w[0];
            for (int i = 1; i < w.length; i++) {
                arr[i] = arr[i - 1] + w[i];
            }
        }
        
        public int pickIndex() {
            rand = new Random();
            int num = rand.nextInt(arr[arr.length - 1]) + 1;
            int left = 0, right = arr.length - 1;
            while (left <= right) {
                int mid = left + (right - left) / 2;
                if (arr[mid] == num) {
                    return mid;
                } else if (arr[mid] < num) {
                    left = mid + 1;
                } else {
                    right = mid - 1;
                }
            }
            return left;
        }
    }
    
    /**
     * Your Solution object will be instantiated and called as such:
     * Solution obj = new Solution(w);
     * int param_1 = obj.pickIndex();
     */
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  • 原文地址:https://www.cnblogs.com/xuanlu/p/12467648.html
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