merge sort

Author: GreyZeng

src/main/java/grey/algorithm/Code_0014_MergeSort.java

@@ -16,16 +16,44 @@
 
 public class Code_0014_MergeSort {
 
+ // merge sort的递归写法
+ public static void sort(int[] arr) {
+ mergeSort(arr, 0, arr.length - 1);
+ }
+
  // 递归解法
- public static void mergeSort1(int[] arr, int l, int r) {
+ public static void mergeSort(int[] arr, int l, int r) {
  if (l >= r) {
  // 终止条件
  return;
  }
- int m = l + ((r - l) >> 1); // 中点位置
- mergeSort1(arr, l, m);
- mergeSort1(arr, m + 1, r);
- merge(arr, l, m, r);
+ int mid = l + ((r - l) >> 1);
+ mergeSort(arr, l, mid);
+ mergeSort(arr, mid + 1, r);
+ merge2(arr, l, mid, r);
+ }
+
+ public static void merge2(int[] arr, int l, int m, int r) {
+ int[] help = new int[r - l + 1];
+ int s = l;
+ int e = m + 1;
+ int i = 0;
+ while (s <= m && e <= r) {
+ if (arr[s] <= arr[e]) {
+ help[i++] = arr[s++];
+ } else {
+ help[i++] = arr[e++];
+ }
+ }
+ while (s <= m) {
+ help[i++] = arr[s++];
+ }
+ while (e <= r) {
+ help[i++] = arr[e++];
+ }
+ for (i = 0; i < help.length; i++) {
+ arr[l++] = help[i];
+ }
  }
 
  // 迭代版本的merge sort
@@ -117,7 +145,7 @@ public static void main(String[] args) {
  int[] copyArray1 = copyArray(arr);
  int[] copyArray2 = copyArray(arr);
  Arrays.sort(arr);
- mergeSort1(copyArray1, 0, copyArray1.length - 1);
+ sort(copyArray1);
  mergeSort2(copyArray2, 0, copyArray2.length - 1);
  if (!sameValue(arr, copyArray1)) {
  System.out.println("出错了！");