java七大排序——7_归并排序

Posted 2022-10-03

归并排序：

将数组分为2块，再到每一小块再分为两块，直到最后一个元素为一块，然后进行有序数组合并，最终合并为一个有序数组
代码实现

public static void mergeSorts ( int[] array)
 mergeSortsInternal(array,0,array.length)
//mergeSortsInternalNoR(array);

/**
* 归并排序：递归内部排序
*/
public static void mergeSortInternal ( int[] array, int low, int high)
if (low + 1 >= high) //[low,high)
return;

int mid = (low + high) / 2;
mergeSortInternal(array, low, mid);
mergeSortInternal(array, mid, high);
merge(array, low, mid, high);

private static void merge ( int[] array, int low, int mid, int high)
int length = high - low;
int[] extral = new int[length];
//[low,mid]
//[mid,high]
int less = low;
int great = mid;
int i = 0;
while (less < mid && great < high) 
if (array[less] <= array[great]) 
extral[i] = array[less];
less++;
i++;
 else 
extral[i] = array[great];
great++;
i++;


while (less < mid) 
extral[i++] = array[less++];

while (great < high) 
extral[i++] = array[great++];

for (int j = 0; j < length; j++) 
array[low + j] = extral[j];