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| import java.util.*;
class Program {
static class MinHeap {
List<Integer> heap = new ArrayList<Integer>();
public MinHeap(List<Integer> array) {
heap = buildHeap(array);
}
public List<Integer> buildHeap(List<Integer> array) {
int firstParent = (array.size() - 2) / 2;
for (int i = firstParent; i >= 0; i--) {
siftDown(i, array.size() - 1, array);
}
return array;
}
public void siftDown(int currentIdx, int endIdx, List<Integer> heap) {
int leftChild = currentIdx * 2 + 1;
while (leftChild < heap.size()) {
int rightChild = (currentIdx * 2 + 2) < heap.size() ? currentIdx * 2 + 2 : -1;
int idxToSwap = leftChild;
if (rightChild != -1 && heap.get(leftChild) > heap.get(rightChild)) {
idxToSwap = rightChild;
}
if (heap.get(currentIdx) > heap.get(idxToSwap)) {
swap(currentIdx, idxToSwap, heap);
currentIdx = idxToSwap;
leftChild = currentIdx * 2 + 1;
} else {
return;
}
}
}
public void siftUp(int currentIdx, List<Integer> heap) {
int parentIdx = (currentIdx - 1) / 2;
while (parentIdx >= 0) {
if (heap.get(currentIdx) < heap.get(parentIdx)) {
swap(currentIdx, parentIdx, heap);
currentIdx = parentIdx;
parentIdx = (currentIdx - 1) / 2;
} else {
return;
}
}
}
public int peek() {
return heap.get(0);
}
public int remove() {
int valueToRemove = heap.get(0);
swap(0, heap.size() - 1, heap);
heap.remove(heap.size() - 1);
siftDown(0, heap.size() - 1, heap);
return valueToRemove;
}
public void insert(int value) {
this.heap.add(value);
siftUp(heap.size() - 1, heap);
}
public void swap(int i, int j, List<Integer> array) {
int temp = array.get(i);
array.set(i, array.get(j));
array.set(j, temp);
}
}
}
|
