398. Random Pick Index

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);

思路： 给了一个数组，包含若干数，可能有重复，然后再给一个数，查找其位置，如果这个数在数组中只出现了一次就返回那个位置，如果不止一次就随机返回一个。

class Solution { private int[] nums; private Random random; public Solution(int[] nums) { this.nums = nums; this.random = new Random(); } public int pick(int target) { int result = -1; int upbound = 1; for (int i = 0; i < nums.length; i++) { if (nums[i] == target) { if (random.nextInt(upbound) == 0) { result = i; } upbound++; } } return result; }}/** * 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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