[LeetCode] 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); Thought process: The question doesn't have a required time complexity on pick, but rather it doesn't allow using too much extra space. The idea is to store the given array as is. Iterate through the array. Use a variable count to keep track of the number of occurrences of target. And use count as an upper bound for random. Solution: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17...