面试常见排序–快速排序的多种实现方法

一、普通方法

	public static int quickSort(int[]array,int low,int high) {
		int i,j,k,t;
		if(low>high) {
			return -1;
		}
		i=low;
		j=high;
		k=array[i];
		while(i<j) {
			while(i<j&&k<=array[j]) {
				j--;
			}
			while(i<j&&k>=array[i]) {
				i++;
			}
			if(i<j) {
				swap(array, i, j);
			}
		}
			array[low]=array[i];
			array[i]=k;
			return i;
			quickSort(array, low, i-1);
			quickSort(array, i+1, high);
	}
		public static void swap(int[] array,int i,int j) {
		int k=array[i];
		array[i]=array[j];
		array[j]=k;
	}

二、首次中轴为随机数

		public static int getMiddle(int[] numbers,int low,int high) {
		int temp=numbers[low];
		while(low<high) {
			while(low<high&&numbers[high]>=temp) {
				high--;
			}
				numbers[low]=numbers[high];
			while(low<high&&numbers[low]<=temp) {
				low++;
			}
				numbers[high]=numbers[low];
			
		}
		numbers[low]=temp;
		return low;
	}
		public static int randPartion(int[]a ,int i,int j) {
		Random random=new Random();
		int l=random.nextInt(j-i)+i;
		swap(a, l,i );
		return getMiddle(a, i, j);
	}
		public static void quickSort2(int[] numbers,int low,int high) {
		if(low<high) {
			int middle=randPartion(numbers, low, high);
			quickSort2(numbers, low, middle-1);
			quickSort2(numbers, middle+1, high);
		}		
	}

三、非递归方法

		public static int getMiddle(int[] numbers,int low,int high) {
		int temp=numbers[low];
		while(low<high) {
			while(low<high&&numbers[high]>=temp) {
				high--;
			}
				numbers[low]=numbers[high];
			while(low<high&&numbers[low]<=temp) {
				low++;
			}
				numbers[high]=numbers[low];
			
		}
		numbers[low]=temp;
		return low;
	}
		public static int randPartion(int[]a ,int i,int j) {
		Random random=new Random();
		int l=random.nextInt(j-i)+i;
		swap(a, l,i );
		return getMiddle(a, i, j);
	}
	public static void quickSort3(int[] numbers,int low,int high) {
		LinkedList<Integer>stack=new LinkedList<>();
		if(low<high) {
			stack.push(low);
			stack.push(high);
			while(!stack.isEmpty()){
				int r=stack.pop();
				int l=stack.pop();
				int middle=quickSort(numbers, l, r);
				if(l<middle-1) {
					stack.push(l);
					stack.push(middle-1);
				}
				if(r>middle+1) {
					stack.push(middle+1);
					stack.push(r);
				}
			}				
		}		
	}