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

Posted 2020-09-22 it_worker365

    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;
    }