归并排序，递归和非递归实现

package com.harrison.class03;

public class Code01_MergeSort {
    
    
	public static void mergeSort1(int[] arr) {
    
    
		if (arr == null || arr.length < 2) {
    
    
			return;
		}
		process(arr, 0, arr.length - 1);
	}

	public static void process(int[] arr, int L, int R) {
    
    
		if (L == R) {
    
    
			return;
		}
		int mid = L + ((R - L) >> 1);
		process(arr, L, mid);
		process(arr, mid + 1, R);
		merge(arr, L, mid, R);
	}

	public static void merge(int[] arr, int L, int M, int R) {
    
    
		int[] help = new int[R - L + 1];
		int i = 0;
		int p1 = L;
		int p2 = M + 1;
		while (p1 <= M && p2 <= R) {
    
    
			help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
		}
		while (p1 <= M) {
    
    
			help[i++] = arr[p1++];
		}
		while (p2 <= R) {
    
    
			help[i++] = arr[p2++];
		}
		for (i = 0; i < help.length; i++) {
    
    
			arr[L+i] = help[i];
		}
	}
	
	public static void mergeSort2(int[] arr) {
    
    
		if (arr == null || arr.length < 2) {
    
    
			return;
		}
		int N=arr.length;
		int mergeSize=1;
		while(mergeSize<N) {
    
    
			int L=0;
			while(L<N) {
    
    
				int M=L+mergeSize-1;
				if(M>=N) {
    
    
					break;
				}
				int R=Math.min(M+mergeSize, N-1);
				merge(arr, L, M, R);
				L=R+1;
			}
			if(mergeSize>N/2) {
    
    
				break;
			}
			mergeSize<<=1;
		}
	}

	public static int[] generateRandomArray(int maxSize, int maxValue) {
    
    
		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
		for (int i = 0; i < arr.length; i++) {
    
    
			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
		}
		return arr;
	}

	public static int[] copyArray(int[] arr) {
    
    
		if (arr == null) {
    
    
			return null;
		}
		int[] res = new int[arr.length];
		for (int i = 0; i < arr.length; i++) {
    
    
			res[i] = arr[i];
		}
		return res;
	}

	public static boolean isEqual(int[] arr1, int[] arr2) {
    
    
		if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
    
    
			return false;
		}
		if (arr1 == null && arr2 == null) {
    
    
			return true;
		}
		if (arr1.length != arr2.length) {
    
    
			return false;
		}
		for (int i = 0; i < arr1.length; i++) {
    
    
			if (arr1[i] != arr2[i]) {
    
    
				return false;
			}
		}
		return true;
	}

	public static void printArray(int[] arr) {
    
    
		if (arr == null) {
    
    
			return;
		}
		for (int i = 0; i < arr.length; i++) {
    
    
			System.out.print(arr[i] + " ");
		}
		System.out.println();
	}
	
	public static void main(String[] args) {
    
    
		int testTimes=1000000;
		int maxSize=100;
		int maxValue=100;
		System.out.println("test begin");
		for(int i=0; i<testTimes; i++) {
    
    
			int[] arr1=generateRandomArray(maxSize, maxValue);
			int[] arr2=copyArray(arr1);
			mergeSort1(arr1);
			mergeSort2(arr2);
			if(!isEqual(arr1, arr2)) {
    
    
				System.out.println("Oops");	
				printArray(arr1);
				printArray(arr2);
				break;
			}
		}
		System.out.println("finish");
	}
}