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QuickSortSolution.java
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69 lines (57 loc) · 1.93 KB
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package sort;
import java.util.ArrayList;
/**
* Created by bruce_shan on 2018/6/4 15:24.
* Description : 快排的应用 返回前K小的数
*/
public class QuickSortSolution {
public void quickSort(int[] array, int left, int right, int k) {
if (left >= right) {
return;
}
int middle = partition(array, left, right);
if (middle < k) {
quickSort(array, middle + 1, right, k);
}
quickSort(array, left, middle - 1, k);
}
// 一次划分过程
private int partition(int[] array, int left, int right) {
int middle = left;
int middleKey = array[middle];
while (left < right) {
// 高指针先走
while (left < right && array[right] > middleKey) { // 高指针找到 <= 中轴的数停下
right--;
}
while (left < right && array[left] <= middleKey) { // 低指针找到 > 中轴的数停下
left++;
}
// 交换高低指针的值
if (left < right) {
array[left] = array[left] ^ array[right];
array[right] = array[left] ^ array[right];
array[left] = array[left] ^ array[right];
}
}
// 将中轴的值放置到中轴位置
if (right > middle) {
array[middle] = array[middle] ^ array[right];
array[right] = array[middle] ^ array[right];
array[middle] = array[middle] ^ array[right];
}
return right;
}
// 快排的应用: 最小的k个数
public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {
ArrayList<Integer> list = new ArrayList<>();
if(k > input.length){
return list;
}
quickSort(input, 0, input.length - 1, k);
for (int i = 0; i < k; i++) {
list.add(input[i]);
}
return list;
}
}