归并排序原理图:
代码:
public static void main(String[] args) {
//int[] arr = {8, 4, 5, 7, 1, 3, 6, 2, 0, 235};
//测试时间 测试时间112mm左右
int[] arr = new int[800000];
int [] temp = new int[arr.length];
for (int a = 0; a < arr.length; a++){
arr[a] = (int)(Math.random() * 80000);
}
Date da1 = new Date();
SimpleDateFormat simpleDateFormat1 = new SimpleDateFormat("yyyy-mm-dd HH:mm:ss--SSS");
String f1 = simpleDateFormat1.format(da1);
System.out.println(f1);
mergeSort(arr, 0, arr.length - 1, temp);
Date da2 = new Date();
SimpleDateFormat simpleDateFormat2 = new SimpleDateFormat("yyyy-mm-dd HH:mm:ss--SSS");
String f2 = simpleDateFormat1.format(da2);
System.out.println(f2);
//System.out.println(Arrays.toString(arr));
}
//分和合
public static void mergeSort(int[] arr, int left, int right, int[] temp){
if (left < right) {
int mid = (left + right) / 2;
//向左递归分解
mergeSort(arr, left, mid, temp);
//向右递归分解
mergeSort(arr, mid +1, right, temp);
//合并
merge(arr, left, mid, right, temp);
}
}
/**
* 合并的方法
* @param arr 数组
* @param left 左边有序序列的初始索引
* @param mid 中间索引
* @param right 右边的索引
*/
public static void merge(int[] arr, int left, int mid, int right, int[] temp){
int i = left;//初始化i,左边有序索引
int j = mid + 1;//初始化j,右边有序索引
int t = 0;//指向temp的当前索引
while (i <= mid && j <= right){
if (arr[i] < arr[j]) {
temp[t] = arr[i];
i += 1;
t += 1;
}else {
temp[t] = arr[j];
j += 1;
t += 1;
}
}
//左边剩余
while (i <= mid) {
temp[t] = arr[i];
i += 1;
t += 1;
}
//右边剩余
while (j <= right) {
temp[t] = arr[j];
j += 1;
t += 1;
}
//将temp的数组元素拷贝到arr
//注意并不是拷贝所有
t = 0;
int tempLeft = left;
while (tempLeft <= right) {
arr[tempLeft] = temp[t];
t += 1;
tempLeft += 1;
}
}