Here is my solution. I used a HashMap in conjunction with quickselection.
Inserting a stock is O(n)
Updating a stock is O(1)
Getting top k stocks (not in sorted order) is O(n) average case
public class StockTicker {
public class Stock{
String sym;
double price;
public Stock(String s, double val){
this.sym = s;
this.price = val;
}
}
HashMap<String,Stock> st;
HashMap<String,Integer> ind;
int unique;
int max;
Stock[] stocks;
public StockTicker(int k){
this.unique = 0;
this.max = k;
this.st = new HashMap<String, Stock>();
this.ind = new HashMap<String, Integer>();
this.stocks = new Stock[k];
}
public void addOrUpdate(String sym, double price){
if(!st.containsKey(sym)){
Stock stock = new Stock(sym,price);
st.put(sym, stock);
ind.put(sym, unique);
stocks[unique++] = stock;
}
else{
Stock update = st.get(sym);
update.price = price;
}
}
public List<Stock> top(int k){
List<Stock> res = new ArrayList<Stock>();
Stock[] temp = new Stock[max];
for(int i = 0; i < temp.length; i++){
temp[i] = new Stock(stocks[i].sym, stocks[i].price);
}
int top = quickselect(temp, 0, temp.length-1, k);
for(int i = 0; i <= top; i++){
res.add(temp[i]);
}
return res;
}
public int quickselect(Stock[] stocks, int left, int right, int kth){
if(left == right){
return left;
}
int split = partition(stocks, left,right);
if(kth-1 == split){ return split;}
else if(kth-1 > split){ return quickselect(stocks,split + 1, right, kth);}
else { return quickselect(stocks, left , split-1, kth);}
}
public int partition(Stock[] stocks, int left, int right){
int lastIndex = right;
double pivot = stocks[lastIndex].price;
while(left <= right){
while( left <= right && stocks[left].price > pivot ){
left++;
}
while( left <= right && stocks[right].price <= pivot){
right--;
}
if(left <= right && stocks[left].price <= pivot && stocks[right].price > pivot){
swap(stocks,left,right);
}
}
swap(stocks,left,lastIndex);
return left;
}
public void swap(Stock[] stocks, int x, int y){
Stock eleX = stocks[x];
Stock eleY = stocks[y];
stocks[x] = eleY;
stocks[y] = eleX;
}
public Stock getStock(String sym){
return st.get(sym);
}
}
'''
