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在乱序数组中找到target的随机index，target可能重复。

时间复杂度：O(N)，空间复杂度：O(1)

public class Solution {        int[] nums;    Random random;        public Solution(int[] nums) {        this.nums = nums;        this.random = new Random();    }        public int pick(int target) {        int count = 1;        int res = -1;        for (int i = 0; i < nums.length; i++) {            if (nums[i] == target) {                if (random.nextInt(count) == count - 1) {                    res = i;                }                count++;            }        }        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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