链表有环判断，快慢指针两种方法/合并链表/删除重复元素/二分递归和while

public static boolean hasCycle(ListNode head) {
if (head == null || head.next == null) {
return false;
}
ListNode slow = head;
ListNode fast = head.next;
while (slow != fast) {
if (slow.next == null)
return false;
slow = slow.next;
if (fast.next == null)
return false;
if (fast.next.next == null)
return false;
fast = fast.next.next;
}
return true;
}
public static boolean hasCycle1(ListNode head) {
if (head == null || head.next == null) {
return false;
}
ListNode slow = head;
ListNode fast = head.next;
while (fast.next != null) {
if (slow == fast) {
return true;
}
slow = slow.next;
if (fast.next.next == null){
return false;
}
fast = fast.next.next;
}
return false;
}

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode result = new ListNode(0);
ListNode head1 = l1;
ListNode head2 = l2;
ListNode resultPoint = result;
while (head1 != null && head2 != null) {
if (head1.val <= head2.val) {
ListNode currNode1 = new ListNode(head1.val);
resultPoint.next = currNode1;
resultPoint = resultPoint.next;
head1 = head1.next;
} else {
ListNode currNode2 = new ListNode(head2.val);
resultPoint.next = currNode2;
resultPoint = resultPoint.next;
head2 = head2.next;
}
}
if (head1 != null) {
resultPoint.next = head1;
}
if (head2 != null) {
resultPoint.next = head2;
}
return result.next;
}
}

public static ListNode deleteDuplicates(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode pre = head;
ListNode curr = head.next;
while (curr != null) {
if (curr.val == pre.val) {
pre.next = curr.next;
} else {
pre = pre.next;
}
curr = curr.next;
}
return head;
}

public static boolean binarySearchDigui(int[] array, int start, int end, int val){
if (start >= end) {
return false;
}
int mid = start + (end - start) / 2;
if (val < array[mid]) {
return binarySearchDigui(array, start, mid, val);
} else if (val > array[mid]){
return binarySearchDigui(array, mid + 1, end, val);
} else {
return true;
}
}
public static boolean binarySearchWhile(int[] array, int start, int end, int val){
while (start < end) {
int mid = start + (end - start) / 2;
if (val < array[mid]) {
end = mid;
} else if (val > array[mid]){
start = mid + 1;
} else {
return true;
}
}
return false;
}