歸併排序穩定
時間複雜度:O(nlogn)
空間複雜度:O(n)
代碼
/**
* @description:歸併排序
* @Author MRyan
* @Date 2020/5/2 20:07
* @Version 1.0
*/
public class Merge_Sort {
// for test
public static void main(String[] args) {
int[] arr = {1, 2, 3, 4, 5};
mergeSort(arr);
print_nums(arr);
}
public static void mergeSort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
mergeSort(arr, 0, arr.length - 1);
}
public static void mergeSort(int[] arr, int l, int r) {
if (l == r) {
return;
}
int mid = (l + r) >> 1;
mergeSort(arr, l, mid);
mergeSort(arr, mid + 1, r);
merge(arr, l, mid, r);
}
/**
* 外排
*
* @param arr
* @param l
* @param m
* @param r
*/
public static void merge(int[] arr, int l, int m, int r) {
int[] help = new int[r - l + 1];
int i = 0;
int p1 = l;
int p2 = m + 1;
while (p1 <= m && p2 <= r) {
help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
}
while (p1 <= m) {
help[i++] = arr[p1++];
}
while (p2 <= r) {
help[i++] = arr[p2++];
}
for (i = 0; i < help.length; i++) {
arr[l + i] = help[i];
}
}
public static void print_nums(int[] nums) {
for (int i : nums) {
System.out.print(i + " ");
}
}
}