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);水塘抽样
class Solution { public: Solution(vector<int> nums) { number = nums; } int pick(int target) { int alpha = 1; int resIndex; for (int i = 0; i < number.size(); ++i) { if (number[i] == target) { if (rand() % alpha == 0) resIndex = i; ++alpha; } } return resIndex; } private: vector<int> number; }; /** * Your Solution object will be instantiated and called as such: * Solution obj = new Solution(nums); * int param_1 = obj.pick(target); */