find K maximum value from an unsorted array(implement min heap)
Maintain a min-heap with size = k, to collect the result.
//Find K minimum values from an unsorted array
//Implement Min-Heap public int[] findKMax(int[] arr, int k){
if(arr == null || arr.length == 0) return null;
int[] result = new int[k];
for(int i = 0; i < k; i ++)
result[i] = arr[i];
buildMinHeap(result);
for(int i = k; i < arr.length; i ++){
if(arr[i] > result[0]){
result[0] = arr[i];
minHeapify(result, 0);
}
}
return result;
} public void buildMinHeap(int[] arr){
for(int i = arr.length / 2 - 1; i > -1; i --){//bottom-up build min heap
minHeapify(arr, i);
}
} public void minHeapify(int[] arr, int curIndex){
int left = curIndex * 2 + 1;
int right = curIndex * 2 + 2;
int smallest = curIndex;
if(left < arr.length && arr[left] < arr[smallest])
smallest = left;
if(right < arr.length && arr[right] < arr[smallest])
smallest = right;
if(smallest != curIndex){
swap(arr, smallest, curIndex);
minHeapify(arr,smallest);
}
} public void swap(int[] arr, int aa, int bb){
int tmp = arr[aa];
arr[aa] = arr[bb];
arr[bb] = tmp;
}
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