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MinHeap.java
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MinHeap.java
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class MinHeap {
private int[] array;
private int size;
public MinHeap(int[] array) {
if (array == null || array.length == 0) {
throw new IllegalArgumentException("input array cannot be null or empty");
}
this.array = array;
size = array.length;
heapify();
}
private void heapify() {
for (int i = size / 2 - 1; i >= 0; i--) {
percolateDown(i);
}
}
public MinHeap(int cap) {
if (cap <= 0) {
throw new IllegalArgumentException("capacity cannot be less than 0");
}
array = new int[cap];
size = 0;
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
private boolean isFull() {
return size == array.length;
}
private void percolateUp(int index) {
while (index > 0) {
int parentIndex = (index - 1) / 2;
if (array[parentIndex] > array[index]) {
swap(array, parentIndex, index);
} else {
break;
}
index = parentIndex;
}
}
private void percolateDown(int index) {
while (index <= size / 2 - 1) {
int leftChildIndex = index * 2 + 1;
int rightChildIndex = index * 2 + 2;
int swapCandidate = leftChildIndex;
if (rightChildIndex <= size - 1 && array[leftChildIndex] >= array[rightChildIndex]) {
swapCandidate = rightChildIndex;
}
if (array[index] > array[swapCandidate]) {
swap(array, index, swapCandidate);
} else {
break;
}
index = swapCandidate;
}
}
private void swap(int[] array, int i, int j) {
int tmp = array[i];
array[i] = array[j];
array[j] = tmp;
}
public int peek() {
if (size == 0) {
throw new IllegalArgumentException("heap is empty");
}
return array[0];
}
public int poll() {
if (size == 0) {
throw new IllegalArgumentException("heap is empty");
}
int res = array[0];
array[0] = array[size - 1];
size--;
percolateDown(0);
return res;
}
public void offer(int element) {
if (size == array.length) {
int[] newArray = new int[(int)(array.length * 1.5)];
for (int i = 0; i < array.length; i++) {
newArray[i] = array[i];
}
array = newArray;
}
array[size] = element;
size++;
percolateUp(size - 1);
}
public int update(int index, int element) {
if (index < 0 || index > size - 1) {
throw new ArrayIndexOutOfBoundsException("invalid index range");
}
int res = array[index];
array[index] = element;
if (res > element) {
percolateUp(index);
} else {
percolateDown(index);
}
return res;
}
}