快排归并

比较重要的两个算法代码实现

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package gurq.sort;

import java.util.Arrays;

/**
* 归并排序
* @author gurq
* @date 2020/11/15 11:46 下午
*/
public class MergeSort {
public static void main(String[] args) {
int[] arr = new int[]{9, 8, 7, 6, 5, 4, 3, 2, 1};
sort(arr);
System.out.println(Arrays.toString(arr));
}

private static void sort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
int[] temp = new int[arr.length];
sort(arr, temp, 0, arr.length - 1);
}

private static void sort(int[] arr, int[] temp, int left, int right) {
if (left >= right) {
return;
}
int mid = (left + right) / 2;
sort(arr, temp, left, mid);
sort(arr, temp, mid + 1, right);
merge(arr, temp, left, mid, right);
}

private static void merge(int[] arr, int[] temp, int left, int mid, int right) {
int a = left;
int b = mid + 1;
int c = 0;

while (a <= mid && b <= right) {
if (arr[a] <= arr[b]) {
temp[c++] = arr[a++];
} else {
temp[c++] = arr[b++];
}
}

while (a <= mid) {
temp[c++] = arr[a++];
}

while (b <= right) {
temp[c++] = arr[b++];
}

c = 0;
while (left <= right) {
arr[left++] = temp[c++];
}
}
}
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package gurq.sort;

import java.util.Arrays;

/**
* 快排
* @author gurq
* @date 2020/11/15 10:22 下午
*/
public class QuickSort {
public static void main(String[] args) {
int[] arr = new int[]{9, 8, 7, 6, 5, 4, 3, 2, 1};
quick(arr);
System.out.println(Arrays.toString(arr));
}

private static void quick(int[] arr){
if (arr == null || arr.length < 2) {
return;
}
sort(arr, 0, arr.length - 1);
}

private static void sort(int[] arr, int left, int right) {
int a = left;
int b = right;
if (a > b) {
return;
}
int c = arr[a];

int temp;
while (a < b) {
while (a < b && arr[b] >= c) {
b--;
}
while (a < b && arr[a] <= c) {
a++;
}
if (a < b) {
temp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
}
}

arr[left] = arr[a];
arr[a] = c;

sort(arr, left, a - 1);
sort(arr, a + 1, right);
}
}

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