LeetCode143 重排链表

题目

解题

解题一：线性表

// javascript
var reorderList = function(head) {
    if (head === null) return;
    const vec = new Array();
    let curr = head;
    while (curr !== null) {
        vec.push(curr);
        curr = curr.next;
    }
    let i = 0; j = vec.length - 1;
    while (i < j) {
        vec[i].next = vec[j];
        i++;
        if (i === j) break;
        vec[j].next = vec[i];
        j--;
    }
    vec[i].next = null;
};

解题二：寻找链表中点 + 链表逆序 + 合并链表

// javascript
var reorderList = function(head) {
    if (head === null) return;
    // 寻找链表中点
    const firstHalfTail = getMiddlenNode(head);
    let secondHalfHead = firstHalfTail.next;
    firstHalfTail.next = null;
    // 链表逆序
    secondHalfHead = reverseList(secondHalfHead);
    // 合并链表
    return mergeLists(head, secondHalfHead);
};

const getMiddlenNode = (head) => {
    let fast = head, slow = head;
    while (fast.next !== null && fast.next.next !== null) {
        slow = slow.next;
        fast = fast.next.next;
    }
    return slow;
};

const reverseList = (head) => {
    let prev = null;
    while (head !== null) {
        const next = head.next;
        head.next = prev;
        prev = head;
        head = next;
    }
    return prev;
};

const mergeLists = (l1, l2) => {
    while (l1 !== null && l2 !== null) {
        const nextl1 = l1.next;
        const nextl2 = l2.next;
        l1.next = l2;
        l1 = nextl1;
        l2.next = l1;
        l2 = nextl2;
    }
};