Some useful methods about linkedList.

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/**
* 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;}//55,22,11,33for (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;}