Java实现归并排序

归并排序

public class MergeSort { /** * 归并排序:时间复杂度为O(n*logn) */ public static void mergeSort(int[] arr, int l, int r) { if (arr == null || arr.length < 2 || l == r) { return; } int mid = l + ((r - l) >> 2); mergeSort(arr, l, mid); mergeSort(arr, mid + 1, r); merge(arr, l, mid, r); } public static void merge(int[] arr, int l, int mid, int r) { int[] help = new int[r - l + 1]; int i = 0; int p1 = l; int p2 = mid + 1; while (p1 <= mid && p2 <= r) { help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++]; } while (p1 <= mid) { 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 main(String[] args) { int[] arr = { 9, 3, 1, 1, 8, 5, 5, 6, 0 }; mergeSort(arr, 0, arr.length - 1); for (int i = 0; i < arr.length; i++) { System.out.println(arr[i]); } } }