算法學習筆記 —— MergeSort 的一種循環實現

public class MergeSort {

	public static void main(String[] args) {
		int[] dealArray = new int[]{11, 22, 5, 3, 6, 1, 10, 7, 8};
		mergeSort(dealArray, 9);//注意此處傳遞的是對象
		for(int i = 0; i < 9; i++) 
			System.out.println(dealArray[i]);
	}
	
	public static void mergeSort(int[] dealArray, int length) {
		int forNum = (int) Math.ceil(Math.log(length));
		for(int i = 0; i <= forNum; i++) {
			int numGrp = (int) Math.pow(2, i);//分組之後每組的元素的個數
			int groupNum = length / numGrp;//分的組數
			int lastNum = length - groupNum * numGrp;
			int len = 2 * numGrp;
			int j = 0;
			for (; j < length - len ; j += len) 
				merge(dealArray, j, j + numGrp -1, j + len -1);
			if (groupNum % 2 == 1 && lastNum != 0) 
				merge(dealArray, j, j + numGrp -1, length - 1);
		}
	}
	
	
	
	public static void merge(int[] dealArray, int lower, int split, int upper) {
		int mark1 = lower;//初始化mark1指向第一個字數組的首元素
		int mark2 = split + 1;//初始化mark2指向第二個字數組的首元素
		int mark = 0;//初始化mark指向臨時數組的首元素
		
		int length = upper - lower + 1;
		int[] tempArray = new int[length];
		while (mark1 <= split && mark2 <= upper) {
			if (dealArray[mark1] <= dealArray[mark2]) 
				tempArray[mark++] = dealArray[mark1++];
			else 
				tempArray[mark++] = dealArray[mark2++];
		}
		while (mark1 <= split) 
			tempArray[mark++] = dealArray[mark1++];
		while (mark2 <= upper) 
			tempArray[mark++] = dealArray[mark2++];
		for(int i = 0; i < length; i++) 
			dealArray[lower + i] = tempArray[i];
	}
}