java排序算法-归并排序

public class MergeSort {



	private static void mergeSortTest() {

		int[] in = { 2, 5, 3, 8, 6, 7, 1, 4, 0, 9 };

		Utils.printArray("归并排序前：",in);

		int a[] = mergeSort(in);

		Utils.printArray("归并排序后：",a);

	}



	private static int[] mergeSort(int[] arr) {

		if (arr.length == 1) {

			return arr;

		} else {

			int[] arrL = new int[arr.length / 2];

			int[] arrR = new int[arr.length - arr.length / 2];

			int mid = arr.length / 2;

			for (int i = 0; i < mid; i++) {

				arrL[i] = arr[i];

			}

			for (int i = mid, j = 0; i < arr.length; i++, j++) {

				arrR[j] = arr[i];

			}

			int[] sortedArrL = mergeSort(arrL);

			int[] sortedArrR = mergeSort(arrR);

			int[] resultArr = mergeTwoArr(sortedArrL, sortedArrR);

			return resultArr;

		}

	}



	private static int[] mergeTwoArr(int[] arrL, int[] arrR) {

		int i = 0, j = 0;

		int[] arrTmp = new int[arrL.length + arrR.length];

		int foot = 0;

		while (i < arrL.length && j < arrR.length) {

			if (arrL[i] <= arrR[j]) {

				arrTmp[foot++] = arrL[i++];

			} else {

				arrTmp[foot++] = arrR[j++];

			}

		}

		if (i == arrL.length) {

			while (j < arrR.length) {

				arrTmp[foot++] = arrR[j++];

			}

		} else {

			while (i < arrL.length) {

				arrTmp[foot++] = arrL[i++];

			}

		}

		return arrTmp;

	}

	

	public static void main(String[] args) {

		mergeSortTest();

	}

}