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  • [LC] 398. Random Pick Index

    Given an array of integers 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.

    Note:
    The array size can be very large. Solution that uses too much extra space will not pass the judge.

    Example:

    int[] nums = new int[] {1,2,3,3,3};
    Solution solution = new Solution(nums);
    
    // pick(3) should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
    solution.pick(3);
    
    // pick(1) should return 0. Since in the array only nums[0] is equal to 1.
    solution.pick(1);

    class Solution {
    
        private int[] arr;
        private Random rand;
        
        public Solution(int[] nums) {
            this.arr = nums;
            this.rand = new Random();
        }
        
        public int pick(int target) {
            int count = 0;
            int res = -1;
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] != target) {
                    continue;
                }
                count += 1;
                int randNum = rand.nextInt(count);
                if (randNum == 0) {
                    res = i;
                }
            }
            return res;
        }
    }
    
    /**
     * Your Solution object will be instantiated and called as such:
     * Solution obj = new Solution(nums);
     * int param_1 = obj.pick(target);
     */
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  • 原文地址:https://www.cnblogs.com/xuanlu/p/12181760.html
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