【DataStructure】Some useful methods about linkedList.

/**
* Method 1: Delete the input element x 
* and meanwhile keep the length of array after deleted n
* @param a  the array
* @param n  the length of array after deleted.
* @param x  the element that need to be deleted. 

*/

static void delete(int[] a, int n, int x) {
		// preconditions: [0] <= ... <= a[n-1], and n <= a.length;
		// postconditions: a[0] <= ... <= a[n-2], and x is deleted;
		int i = 0; // find the first index i for which a[i] > x:
		while (i < n && a[i] <= x) {
			++i;
		}
		// shift {a[i],...,a[n-1]} into {a[i-1],...,a[n-2]}:
		if (i < n - 1) {
			System.arraycopy(a, i, a, i - 1, n - i);
		}
		a[n - 1] = 0;
	}

/**
* Gets the number of nodes in the specified list;
* Fox example, if list is {33,55,77,99}, the size(list) will be return 4;
* 
* @param list 
* @return
*/

static int size(Node list) {
		int size = 0;
		while (list != null) {
			++ size;
			list = list.next;
		}
		
		return size;
	}

/**
* Gets the sum of nodes in the specified list;
* Fox example, if list is {33,55,77,99}, the size(list) will be return 254;
* @param list
* @return
*/

static int sum(Node list){
		int sum = 0;
		while(list != null){
			sum += list.data;
			list = list.next;
		}
		
		return sum;
	}

/**
// precondition: the specified list has at least two nodes;
// postcondition: the last node in the list has been deleted;
For example, if list is {22, 44, 66, 88}, then removeLast(list)will change it to {22, 44,66}.
* @param list
*/

void removeLast(Node list){
		if(list == null || list.next == null)
		{
			//throw new IllegalStatException();
		}
		//{33,55,77,99} 
		
		
		while(list.next.next != null) {
			list = list.next;
		}
		
		list.next = null;
	} 

/**
* 
* @param list
* @return
*/

static Node copy(Node list)
	{
		if(list == null)
		{
			return null;
		}
		
		Node clone = new Node(list.data);
		for (Node p = list, q = clone; p != null; p = p.next, q = q.next)
		{
			q.next = p.next;
		}
		
		return clone;
	}
	

/**
* Get a new list that contains copies of the p-q nodes of the specified list, 
* starting with node number p(starting with 0).
* For example, if listis {22, 33, 44, 55, 66, 77, 88, 99}, then sublist(list, 2, 7)will
* return the new list {44, 55, 66, 77, 88}. Note that the two lists must be completely independent of each other.
* Changing one list should have no effect upon the other.
* @param list
* @param m
* @param n
* @return
*/

Node sublist(Node list, int m, int n) {
		if (m < 0 || n < m) {
			throw new IllegalArgumentException();
		} else if (n == m) {
			return null;
		}
		
		//55,22,11,33
		for (int i = 0; i < m; i++) {
			list = list.next;
		}
		Node clone = new Node(list.data);
		Node p = list, q = clone;
		for (int i = m + 1; i < n; i++) {
			if (p.next == null) {
				throw new IllegalArgumentException();
			}
			q.next = new Node(p.next.data);
			p = p.next;
			q = q.next;
		}
		return clone;
	}