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295.cpp
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132 lines (118 loc) · 3.38 KB
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// Author: btjanaka (Bryon Tjanaka)
// Problem: (Leetcode) 295
// Title: Find Median from Data Stream
// Link: https://leetcode.com/problems/find-median-from-data-stream
// Idea: Typically, this is implemented with two heaps. I decided to use a skip
// list.
// Difficulty: medium
// Tags: implementation
// Skip list
class MedianFinder {
public:
/** initialize your data structure here. */
MedianFinder()
: device_(),
engine_(device_()),
choice_(0, 1),
size_(0u),
heads_(1, new node()),
median_(heads_[0]) {}
void addNum(int num) {
insert(num, heads_.size() - 1, heads_.back());
++size_;
if (median_ == heads_[0]) {
median_ = heads_[0]->next;
} else {
if (size_ % 2 == 1) {
if (num >= median_->val) {
median_ = median_->next;
} else {
// do nothing
}
} else {
if (num >= median_->val) {
// do nothing
} else {
median_ = median_->prev;
}
}
}
}
double findMedian() {
/*printf("BEGIN\n");
for(int i = heads_.size() - 1; i >= 0; --i) {
for(node* cur = heads_[i]->next; cur != nullptr; cur = cur->next) {
printf("%d ", cur->val);
if(i != 0) printf("(%dv) ", cur->below->val);
}
printf("\n");
}
printf("END\n");
printf("%d\n", median_->val);
*/
if (size_ == 0) {
return 0.0;
} else if (size_ % 2 == 0) {
return double(median_->val + median_->next->val) / 2.0;
} else {
return median_->val;
}
}
private:
struct node {
int val;
node* prev;
node* next;
node* below;
node() : val(0), prev(nullptr), next(nullptr), below(nullptr) {}
node(int _val, node* _prev, node* _next, node* _below)
: val(_val), prev(_prev), next(_next), below(_below) {}
};
// randomness for skip list
random_device device_;
default_random_engine engine_;
uniform_int_distribution<int> choice_;
unsigned int size_;
vector<node*> heads_;
node* median_;
node* insert(int num, int lvl, node* cur) {
// Advance while less than or equal to next - thuse we always add duplicates
// to the end of the duplicates
for (; cur->next && cur->next->val <= num; cur = cur->next)
;
node* ret;
// Always add on bottom
if (lvl == 0) {
node* newnode = new node(num, cur, cur->next, nullptr);
if (cur->next) cur->next->prev = newnode;
cur->next = newnode;
ret = cur->next;
} else {
// Add onto this level only if the choice works and the below levels
// worked too
node* below = insert(num, lvl - 1, cur->below);
if (choice_(engine_) && below) {
node* newnode = new node(num, cur, cur->next, below);
if (cur->next) cur->next->prev = newnode;
cur->next = newnode;
ret = cur->next;
} else {
ret = nullptr; // prevents higher levels
}
}
// Possibly add on more levels above
if (lvl == heads_.size() - 1) {
while (ret && choice_(engine_)) {
heads_.push_back(new node(num, nullptr, nullptr, heads_.back()));
ret = heads_.back()->next = new node(num, heads_.back(), nullptr, ret);
}
}
return ret;
}
};
/**
* Your MedianFinder object will be instantiated and called as such:
* MedianFinder obj = new MedianFinder();
* obj.addNum(num);
* double param_2 = obj.findMedian();
*/