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MergeSortedArray.java
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157 lines (125 loc) · 4.27 KB
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import java.util.ArrayList;
import java.util.Arrays;
import java.util.Queue;
import java.util.LinkedList;
/**
* merge K sorted arrays into one. total: N
* min heap: O(NlgK)
*/
public class MergeSortedArray {
private static class ArrayNode {
public Integer value;
public int arrayIndex;
public ArrayNode(Integer v, int index) {
value = v;
arrayIndex = index;
}
public String toString() {
return String.valueOf(value);
}
} // end of ArrayNode
private static class MinHeapArrayNode {
private ArrayList<ArrayNode> heap;
public MinHeapArrayNode() {
heap = new ArrayList<ArrayNode>();
// 1 is the min one.
// it is easy to calculate left, right and parent
heap.add(null);
}
public void insert(ArrayNode node) {
if(node == null)
throw new RuntimeException("can't insert null node");
heap.add(node);
shiftUp(heap.size() - 1);
}
public ArrayNode removeMin() {
if (isEmpty())
throw new RuntimeException("heap is empty");
// System.out.println(heap.toString());
ArrayNode min = heap.get(1);
heap.remove(min);
if (heap.size() != 1) {
shiftDown(1);
}
return min;
}
private void shiftUp(int k) {
//k/2 parent
while (k > 1 && greater(k / 2, k)) {
swap(k / 2, k);
k = k / 2;
}
}
private void shiftDown(int k) {
while (2 * k <= heap.size() - 1) {
int i = 2 * k; //left
int j = i + 1; //right
//find the smallest of left and right
if (i < heap.size() - 1 && greater(i, j)) {
i++; // i = j;
}
if (greater(i, k)) break;
swap(i, k);
k = i;
}
}
private boolean greater(int i, int j) {
if (i > 0 && j < heap.size()) {
return heap.get(i).value > heap.get(j).value;
}
return false;
}
private void swap(int i, int j) {
ArrayNode tmp = heap.get(i);
heap.set(i, heap.get(j));
heap.set(j, tmp);
}
private boolean isEmpty() {
return heap.size() == 1;
}
} // end of MinHeapArrayNode
public static void main(String[] args) {
Integer[][] arrays = new Integer[][]{
{1, 5, 9},
{4, 8, 10,13},
{6, 11},
{2,7}
};
ArrayList<Integer> result = mergeSortedArray(arrays);
System.out.println(result.toString());
}
public static ArrayList<Integer> mergeSortedArray(Integer[][] arrays) {
ArrayList<Integer> result = new ArrayList<Integer>();
ArrayList<Queue<Integer>> lists = new ArrayList<Queue<Integer>>();
for (int i = 0; i < arrays.length; i++) {
ArrayList<Integer> tmpArray = new ArrayList<Integer>(Arrays.asList(arrays[i]));
Queue<Integer> tmpQueue = new LinkedList<Integer>(tmpArray);
lists.add(tmpQueue);
}
MinHeapArrayNode heap = new MinHeapArrayNode();
// initialize minheap
for (int i = 0; i < lists.size(); i++) {
heap.insert(new ArrayNode(lists.get(i).poll(), i));
}
boolean done = false;
while (!done) {
ArrayNode minNode = heap.removeMin();
result.add(minNode.value);
int nextIndex = minNode.arrayIndex;
Queue<Integer> nextQueue = lists.get(nextIndex);
while (nextQueue.size() == 0) {
nextIndex = (nextIndex < lists.size() - 1) ? nextIndex + 1 : 0;
nextQueue = lists.get(nextIndex);
if (nextIndex == minNode.arrayIndex) {
done = true;
break;
}
}
if (!done)
heap.insert(new ArrayNode(nextQueue.poll(), nextIndex));
}
while (!heap.isEmpty())
result.add(heap.removeMin().value);
return result;
}
}