基本排序算法Java实现——归并排序

Posted 2020-09-03 Emma_Zhang

归并排序：升序排

private <T extends Comparable<? super T>> void mergeSortByAsc(T[] data, int low,int high) {
		T[] temp;
		/** 如果左右相等，则返回 */
		if(low == high)
			return;
		/** 找到长度和中间的那个数*/
		int size = high - low +1;
		int mid = (low + high)/2;
		temp = (T[])(new Comparable[size]);
		
		/** 对左边的数据进行排序*/
		mergeSort(data, low, mid);
		
		/** 对右边的数据进行排序*/
		mergeSort(data, mid + 1, high);
		
		/** copy 排序的数组*/
		for(int i = 0;i < size; i++){
			temp[i] = data[low + i];
		}
		/** 合并两个排序的数组*/
		int left = 0;
		int right  = mid - low + 1;
		for(int i = 0; i < size; i++){
			if(right <= high - low){
				if(left <= mid - low){
					if(temp[left].compareTo(temp[right]) > 0){
						data[i + low] = temp[right ++ ];
					}else{
						data[i + low] = temp[left ++];
					}
				}else{
					data[i + low] = temp[right ++ ];
				}
			}else{
				data[i + low] = temp[left ++];
			}
		}
		
	}

　降序排：

　

private <T extends Comparable<? super T>> void mergeSortByDesc(T[] data, int low,int high) {
		T[] temp;
		/** 如果左右相等，则返回 */
		if(low == high)
			return;
		/** 找到长度和中间的那个数*/
		int size = high - low +1;
		int mid = (low + high)/2;
		temp = (T[])(new Comparable[size]);
		
		/** 对左边的数据进行排序*/
		mergeSortByDesc(data, low, mid);
		
		/** 对右边的数据进行排序*/
		mergeSortByDesc(data, mid + 1, high);
		
		/** copy 排序的数组*/
		for(int i = 0;i < size; i++){
			temp[i] = data[low + i];
		}
		/** 合并两个排序的数组*/
		int left = 0;
		int right  = mid - low + 1;
		for(int i = 0; i < size; i++){
			if(right <= high - low){
				if(left <= mid - low){
					if(temp[left].compareTo(temp[right]) < 0){
						data[i + low] = temp[right ++ ];
					}else{
						data[i + low] = temp[left ++];
					}
				}else{
					data[i + low] = temp[right ++ ];
				}
			}else{
				data[i + low] = temp[left ++];
			}
		}
		
	}