https://leetcode.com/problems/random-pick-index/
public class Solution {
private Map mp;
private Random rand;
public Solution(int[] nums) {
mp = new HashMap();
for (int i=0; i<nums.length; i++) {
List lt = (ArrayList)mp.remove(nums[i]);
if (lt == null) {
lt = new ArrayList();
}
lt.add(i);
mp.put(nums[i], lt);
}
rand = new Random();
}
public int pick(int target) {
List lt = (ArrayList)mp.get(target);
return (int)lt.get(rand.nextInt(lt.size()));
}
}
/**
* Your Solution object will be instantiated and called as such:
* Solution obj = new Solution(nums);
* int param_1 = obj.pick(target);
*/
