package test;import java.util.ArrayList;
import java.util.Comparator;
import java.util.PriorityQueue;import org.junit.Test;public class GetLeastNumbers_Solution {/*** 基于优先队列，时间复杂度为o(nlogk)* * @param input* @param k* @return*/public ArrayList<Integer> GetLeastNumbers_SolutionPriorityQuene(int[] input, int k) {ArrayList<Integer> result = new ArrayList<Integer>();if (input == null || input.length == 0 || k <= 0 || k > input.length)return result;PriorityQueue<Integer> maxHeap = new PriorityQueue<Integer>(new Comparator<Integer>() {@Overridepublic int compare(Integer o1, Integer o2) {return o2.compareTo(o1);}});for (int i = 0; i < k; i++) {maxHeap.offer(input[i]);}for (int j = k; j < input.length; j++) {if (input[j] < maxHeap.peek()) {maxHeap.poll();maxHeap.offer(input[j]);}}for (Integer integer : maxHeap) {result.add(integer);}return result;}/*** 基于堆排序,时间复杂度为o(nlogk)* * @param input* @param k* @return*/public ArrayList<Integer> GetLeastNumbers_SolutionMaxHeap(int[] input, int k) {ArrayList<Integer> result = new ArrayList<Integer>();if (input == null || input.length == 0 || k <= 0 || k > input.length)return result;//构建最大堆builtMaxHeap(input,k-1);for (int i = k; i < input.length; i++) {//数组k位后的数字比堆顶小if (input[k] < input[0]) {input[0] = input[k];//调整堆builtMaxHeap(input, k - 1);}}for (int i = 0; i < k; i++) {result.add(input[i]);}return result;}/*** 构建、调整最大堆* @param a* @param lastIndex*/public void builtMaxHeap(int[]a,int lastIndex){int parentIndex = ((lastIndex-1) >> 1);//从最后一个节点的父节点开始for(int i=parentIndex;i>=0;i--){//存在子节点while (i*2+1<=lastIndex){int leftIndex = i*2+1;int rightIndex = i*2+2;int biggerIndex = leftIndex;//存在右结点if (rightIndex <= lastIndex){if(a[rightIndex] > a[biggerIndex]){biggerIndex = rightIndex;}}//子节点中最大节点大于父节点if (a[biggerIndex] > a[i]){swap(a,i,biggerIndex);i = biggerIndex;}else{break;}}}}/*** 基于Partition函数,时间复杂度为o(n),原数组已被修改* * @param input* @param k* @return*/public ArrayList<Integer> GetLeastNumbers_SolutionPartition(int[] input,int k) {ArrayList<Integer> result = new ArrayList<Integer>();if (input == null || input.length == 0 || k <= 0 || k > input.length)return result;int left = 0;int right = input.length - 1;int index = partition(input, 0, right);while (index != k - 1) {if (index > k - 1) {right = index - 1;index = partition(input, left, right);} else {left = index + 1;index = partition(input, left, right);}}for (int i = 0; i < k; i++) {result.add(input[i]);}return result;}/*** partition函数* @param a* @param left* @param right* @return*/public int partition(int[] a, int left, int right) {while (left < right) {while (left < right && a[left] <= a[right]) {right--;}if (left < right) {swap(a, left, right);}while (left < right && a[left] <= a[right]) {left++;}if (left < right) {swap(a, left, right);}}return left;}public void swap(int[] a, int i, int j) {int tmp = a[i];a[i] = a[j];a[j] = tmp;}@Testpublic void testGetLeastNumbers_Solution() {int[] a = { 4, 5, 1, 6, 2, 7, 3, 8 };int k = 4;ArrayList<Integer> list = GetLeastNumbers_SolutionPartition(a, k);System.out.println(list.toString());ArrayList<Integer> list2 = GetLeastNumbers_SolutionPriorityQuene(a, k);System.out.println(list2.toString());ArrayList<Integer> list3 = GetLeastNumbers_SolutionMaxHeap(a, k);System.out.println(list3.toString());}
}