我在应用程序中具有以下合并代码。当未满足IF条件时,我对递归方法如何再次打电话给我感到非常困惑。
我调试了我的代码,但我仍然没有得到它。调用Mergesort(0,number -1)的排序方法首先在Mergesort(0,5)开始。低于高,中间为2,因此接下来运行Mergesort(0,2)。这一直持续到我们有Mergesort(0,0),在这种情况下,低不小于高,因此,它来自IF块。但是当我调试时,该方法返回,并在Mergesort(0,0)案例之后再次开始。呼叫如何再次发生?
public class MergeSort {
private int[] numbers;
private int[] helper;
private int number;
public int[] sort(int[] values) {
this.numbers = values;
number = values.length;
this.helper = new int[number];
return mergesort(0, number - 1);
}
private int[] mergesort(int low, int high) {
// check if low is smaller then high, if not then the array is sorted
if (low < high) {
// Get the index of the element which is in the middle
int middle = low + (high - low) / 2;
// Sort the left side of the array
mergesort(low, middle);
// Sort the right side of the array
mergesort(middle + 1, high);
// Combine them both
merge(low, middle, high);
}
return numbers;
}
private int[] merge(int low, int middle, int high) {
// Copy both parts into the helper array
for (int i = low; i <= high; i++) {
helper[i] = numbers[i];
}
int i = low;
int j = middle + 1;
int k = low;
// Copy the smallest values from either the left or the right side back
// to the original array
while (i <= middle && j <= high) {
if (helper[i] <= helper[j]) {
numbers[k] = helper[i];
i++;
} else {
numbers[k] = helper[j];
j++;
}
k++;
}
// Copy the rest of the left side of the array into the target array
while (i <= middle) {
numbers[k] = helper[i];
k++;
i++;
}
return numbers;
}
}
这是因为mergesort
方法两次调用。您可以打印出堆栈以查看会发生什么。
例如,当调用mergesort(0,1)
时,该方法将首先调用mergesort(0,0)
,然后将mergesort(1,1)
。