代码随想录算法训练营第三天| 203.移除链表元素、707. 设计链表、206.反转链表

203.移除链表元素

707.设计链表

206.反转链表

var removeElements = function(head, val) {
    const dummyHead = new ListNode(-1, head);
    let p0 = dummyHead, p1 = head;

    while(p1) {
        if (p1.val === val) {
            const next = p1.next;
            p1.next = null;
            p1 = next;
            p0.next = p1;
        } else {
            p0 = p0.next;
            p1 = p1.next;
        }

    }

    return dummyHead.next;
};

var ListNode = function(val, next) {
    this.next = next ? next : null;
    this.val = !!val ? val : 0;
}

var MyLinkedList = function() {
    this.dummyHead = new ListNode(-1, null);
    this.listLen = 0;
};

/** 
 * @param {number} index
 * @return {number}
 */
MyLinkedList.prototype.get = function(index) {
    if (index < 0 || index >= this.listLen)  return -1;

    let p = this.dummyHead;
    for (let i=0; i<=index; i++) {
        p = p.next;
    }

    return p.val;
};

/** 
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtHead = function(val) {
    const newNode = new ListNode(val);

    const currHead = this.dummyHead.next;
    this.dummyHead.next = newNode;
    newNode.next = currHead;
    this.listLen += 1;
};

/** 
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtTail = function(val) {
    const newNode = new ListNode(val);

    let tail = this.dummyHead;
    while (tail.next) {
        tail = tail.next;
    }
    tail.next = newNode;
    this.listLen += 1;
};

/** 
 * @param {number} index 
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtIndex = function(index, val) {
    if (index > this.listLen)   return;

    if (index === 0) {
        return this.addAtHead(val);
    }
    if (index === this.listLen) {
        return this.addAtTail(val);
    }

    const newNode = new ListNode(val);
    let p = this.dummyHead;
    for (let i=0; i<index; i++) {
        p = p.next;
    }

    const nextNode = p.next;
    p.next = newNode;
    newNode.next = nextNode;

    this.listLen += 1;
};

/** 
 * @param {number} index
 * @return {void}
 */
MyLinkedList.prototype.deleteAtIndex = function(index) {
    if (index < 0 || index >= this.listLen) return;

    let p = this.dummyHead;
    for (let i=0; i<index; i++) {
        p = p.next;
    }
    const newNext = p.next.next;
    p.next = null;
    p.next = newNext;
    this.listLen -= 1;
};

var reverseList = function(head) {
    let p0 = head, p1 = head?.next;
    if (p1) p0.next = null;
    while(p1) {
        const newNext = p1.next;
        p1.next = p0;
        p0 = p1;
        p1 = newNext;
    }

    return p0;
};