链表算法题

function reverseList(pHead)
{
    let prev = null;
    let curr = pHead;
    while (curr) {
        const next = curr.next;
        curr.next = prev;
        prev = curr;
        curr = next;
    }
    return prev;
}

var swapPairs = function(head) {
    let dummyNode = new ListNode(0);
    dummyNode.next = head;
    let temp = dummyNode;
    while (temp.next != null && temp.next.next != null) {
        let head1 = temp.next;
        let head2 = temp.next.next;
        temp.next = head2;
        head1.next = head2.next;
        head2.next = head1;
        temp = head1;
    }
    return dummyNode.next;
};

function hasCycle( head ) {
    if (head == null) {
        return false;
    }
    let slow = head;
    let fast = head;
    while (fast.next && fast.next.next) {
        slow = slow.next;
        fast = fast.next.next;
        if (slow == fast) {
            return true;
        }
    }
    return false;
}

function detectCycle( head ) {
    if (!head) return null;
    let slow = head, fast = head;
    while(fast.next && fast.next.next) {
        fast = fast.next.next
        slow = slow.next
        if (slow == fast) {
            var a = head;
            while (slow != a) {
                a = a.next
                slow = slow.next
            }
            return a;
        }
    }
    return null;
}

function FindKthToTail( pHead ,  k ) {
    let length = getLength(pHead);
    if (length < k) {
        return null;
    }
    let i = length - k;
    let p = pHead;
    while (i > 0) {
        p = p.next;
        i--;
    }
    return p;
}

var getLength = function( pHead ) {
    let p = pHead;
    let length = 0;
    while (p != null) {
        p = p.next;
        length++;
    }
    return length;
}

function removeNthFromEnd( head ,  n ) {
    let length = getLength(head);
    if (length < n) {
        return null;
    }
    let i = length - n;
    let dummy = new ListNode(0);
    dummy.next = head;
    let p = dummy;
    while (i > 0) {
        p = p.next;
        i--;
    }
    p.next = p.next.next;
    return dummy.next;
}

var getLength = function ( head ) {
    let length = 0;
    let p = head;
    while (p != null) {
        p = p.next;
        length ++;
    }
    return length;
}

function deleteDuplicates( head ) {
    let p = head;
    while (p != null && p.next != null) {
        if (p.val == p.next.val) {
            p.next = p.next.next;
        } else {
            p = p.next;
        }
    }
    return head;
}

function FindFirstCommonNode(pHead1, pHead2)
{
    if (pHead1 == null || pHead2 == null) {
        return null;
    }
    let p1 = pHead1, p2 = pHead2;
    while (p1 != p2) {
        p1 = p1 == null ? pHead2 : p1.next;
        p2 = p2 == null ? pHead1 : p2.next;
    }
    return p1;
}

function mergeTwoLists( l1 ,  l2 ) {
    let newHead = new ListNode(-1);
    let p = newHead;
    while(l1 != null && l2 != null) {
        if (l1.val < l2.val) {
            p.next = l1;
            l1 = l1.next;
        } else {
            p.next = l2;
            l2 = l2.next;
        }
        p = p.next;
    }
    if (l1 != null) {
        p.next = l1;
    }
    if (l2 != null) {
        p.next = l2;
    };
    return newHead.next;
}