剑指 Offer 52. 两个链表的第一个公共节点

方法一 双指针

遍历A,B两个链表，第一次走完当前链表时接着遍历另一个链表，这样两个链表最终会在公共节点汇合。总路程都是(b - c + a - c + c)

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} headA
 * @param {ListNode} headB
 * @return {ListNode}
 */
var getIntersectionNode = function(headA, headB) {
    let A = headA, B = headB;
    while(A != B) {
        A = A == null ? headB : A.next;
        B = B == null ? headA : B.next;
    }
    return A;
};

 

方法二 哈希表

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} headA
 * @param {ListNode} headB
 * @return {ListNode}
 */
var getIntersectionNode = function(headA, headB) {
    const visited = new Set();
    let temp = headA;
    while (temp !== null) {
        visited.add(temp);
        temp = temp.next;
    }
    temp = headB;
    while (temp !== null) {
        if (visited.has(temp)) {
            return temp;
        }
        temp = temp.next;
    }
    return null;
};