import java.util.Arrays;
public class MaxTopK {
public static void main(String[] args) {
int testTime = 500000;
int maxSize = 100;
int maxValue = 100;
boolean pass = true;
System.out.println("测试开始,没有打印出错信息说明测试通过");
for (int i = 0; i < testTime; i++) {
int k = (int) (Math.random() * maxSize) + 1;
int[] arr = generateRandomArray(maxSize,maxValue);
int[] arr1 = copyArray(arr);
int[] arr2 = copyArray(arr);
int[] ans1 = maxTopK1(arr1,k);
int[] ans2 = maxTopK2(arr2,k);
if(!isEqual(ans1,ans2)){
pass = false;
System.out.println("出错了!");
printArray(ans1);
printArray(ans2);
break;
}
}
System.out.println("测试结束了,测试了" + testTime + "组,是否所有测试用例都通过?" + (pass ? "是" : "否"));
}
public static void printArray(int[] arr){
if(arr == null){
return;
}
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i]+" ");
}
System.out.println();
}
public static boolean isEqual(int[] arr1, int[] arr2){
if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
return false;
}
if (arr1 == null && arr2 == null) {
return true;
}
if (arr1.length != arr2.length){
return false;
}
for (int i = 0; i < arr1.length; i++) {
if(arr1[i] != arr2[i]){
return false;
}
}
return true;
}
public static int[] generateRandomArray(int maxSize, int maxValue){
int[] arr = new int[(int)((maxSize+1) * Math.random())];
for (int i = 0; i < arr.length; i++) {
arr[i] = (int)((maxValue+1) * Math.random()) - (int)((maxValue) * Math.random());
}
return arr;
}
public static int[] maxTopK1(int[] arr,int k){
if(arr == null || arr.length == 0){
return new int[0];
}
int N = arr.length;
k = Math.min(N, k);
Arrays.sort(arr);
int[] ans = new int[k];
for (int i = arr.length-1,j = 0; i >= arr.length-k; i--,j++) {
ans[j] = arr[i];
}
return ans;
}
public static int[] maxTopK2(int[] arr,int k){
if(arr == null || arr.length == 0){
return new int[0];
}
int N = arr.length;
k = Math.min(N, k);
int v = minKth3(arr,arr.length - k+1);
int[] ans = new int[k];
int j=0;
for (int i = 0; i < arr.length; i++) {
if(arr[i] > v){
ans[j++] = arr[i];
}
}
for (; j < ans.length; j++) {
ans[j] = v;
}
Arrays.sort(ans);
for (int L = 0, R = k - 1; L < R; L++,R--) {
swap(ans,L,R);
}
return ans;
}
public static int[] copyArray(int[] arr){
int[] ans = new int[arr.length];
for (int i = 0; i < ans.length; i++) {
ans[i] = arr[i];
}
return ans;
}
/*
* bfprt算法
* 1. 5个数一组,排序
* 2. 把每组的中位数拿出来,再组成一个数组arr
* 3. 取出arr数组的中位数p
*/
public static int minKth3(int[] array, int k) {
int[] arr = copyArray(array);
return bfprt(arr,0,arr.length-1,k-1);
}
public static int bfprt(int[] arr, int L, int R, int index){
if(L == R){
return arr[L];
}
int pivot = medianOfMedians(arr, L, R);
int[] range = partition(arr, L, R, pivot);
if(range[0] <= index && index <= range[1]){
return arr[index];
}else if(index < range[0]){
return bfprt(arr, L, range[0]-1, index);
}else{
return bfprt(arr,range[1]+1, R, index);
}
}
// 取出中位数的中位数
public static int medianOfMedians(int[] arr, int L, int R){
int size = R - L + 1;
int offset = size % 5 == 0 ? 0 : 1;
int[] mArr = new int[size/5 + offset];
for (int i = 0; i < mArr.length; i++) {
int teamFirst = L + i * 5;
mArr[i] = getMedian(arr, teamFirst, Math.min(R, teamFirst + 4));
}
return bfprt(mArr,0,mArr.length-1,mArr.length/2);
}
public static int getMedian(int[] arr, int L, int R){
// 插入排序
insertionSort(arr, L, R);
return arr[(R+L)/2];
}
public static void insertionSort(int [] arr, int L, int R){
for (int i = L+1; i <= R; i++) {
for (int j = i-1; j >=L && arr[j] > arr[j+1]; j--) {
swap(arr,j,j+1);
}
}
}
public static int[] partition(int[] arr, int L, int R, int pivot){
int less = L - 1;
int cur = L;
int more = R + 1;
while(cur < more){
if(arr[cur] < pivot){
swap(arr, ++less, cur++);
}else if(arr[cur] > pivot){
swap(arr,cur, --more);
}else{
cur++;
}
}
return new int[]{less+1, more-1};
}
public static void swap(int[] arr, int i1, int i2){
int temp = arr[i2];
arr[i2] = arr[i1];
arr[i1] = temp;
}
}