FB面经Prepare: Merge K sorted Array
Merge K sorted Array
跟Merge K sorted lists不同在于,从PQ里poll出来以后不知道下一个需要被加入PQ的是哪一个
所以需要写一个wrapper class
package fbPractise; import java.util.*; public class MergeKLists {
static class Pair {
int listIndex;
int idInList;
int value;
public Pair(int l, int id, int val) {
this.listIndex = l;
this.idInList = id;
this.value = val;
}
} public static List<Integer> merge(List<List<Integer>> lists) {
List<Integer> res = new ArrayList<Integer>(); Comparator<Pair> comp = new Comparator<Pair>() {
public int compare(Pair p1, Pair p2) {
return p1.value - p2.value;
}
};
PriorityQueue<Pair> pq = new PriorityQueue<Pair>(1, comp);
for (int i=0; i<lists.size(); i++) {
Pair p = new Pair(i, 0, lists.get(i).get(0));
pq.offer(p);
} while (!pq.isEmpty()) {
Pair pa = pq.poll();
int index = pa.listIndex;
int id = pa.idInList;
if (id < lists.get(index).size()-1) {
pq.offer(new Pair(index, id+1, lists.get(index).get(id+1)));
}
res.add(pa.value);
} return res;
} /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
List<Integer> l1 = Arrays.asList(1,2,2,3,6);
List<Integer> l2 = Arrays.asList(1,4,5,7,8,9);
List<Integer> l3 = Arrays.asList(3,3,3,5,10);
List<List<Integer>> lists = new ArrayList<List<Integer>>();
lists.add(new ArrayList<Integer>(l1));
lists.add(new ArrayList<Integer>(l2));
lists.add(new ArrayList<Integer>(l3));
List<Integer> res = merge(lists);
System.out.println(res);
} }
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