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);
``````

``````class Solution {
public:
Solution(vector<int> nums): v(nums) {}

int pick(int target) {
int cnt = 0, res = -1;
for (int i = 0; i < v.size(); ++i) {
if (v[i] != target) continue;
++cnt;
if (rand() % cnt == 0) res = i;
}
return res;
}
private:
vector<int> v;
};
``````

Shuffle an Array

https://discuss.leetcode.com/topic/58371/c-o-n-solution/2

https://discuss.leetcode.com/topic/58297/share-c-o-n-time-solution/2

https://discuss.leetcode.com/topic/58403/bruce-force-java-with-o-n-time-o-1-space

LeetCode All in One 题目讲解汇总(持续更新中…)

 微信打赏 Venmo 打赏
（欢迎加入博主的知识星球，博主将及时答疑解惑，并分享刷题经验与总结，试运营期间前五十位可享受半价优惠～）

×

Help us with donation