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);
A:
class Solution { public: Solution(vector<int>& nums) { for(int i =0;i<nums.size();i++){ M[nums[i]].push_back(i); } } int pick(int target) { auto& tmp = M[target]; int size = tmp.size(); int index = rand()% size; return tmp[index]; } private: unordered_map<int, vector<int>> M; }; /** * 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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