题解 | #两个链表的第一个公共结点#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        //这种情况没有公共节点
        if (pHead1 == null || pHead2 == null) {
            return null;
        }

        ListNode h1 = pHead1;
        ListNode h2 = pHead2;

        int len1 = 0;
        int len2 = 0;

        //遍历以获取长度
        while (h1 != null) {
            h1 = h1.next;
            len1++;
        }
        while (h2 != null) {
            h2 = h2.next;
            len2++;
        }

        //求出长短差值
        int diff = 0;
        ListNode longList, shortList;
        if (len1 > len2) {
            longList = pHead1;
            shortList = pHead2;
            diff = len1 - len2;
        } else {
            shortList = pHead1;
            longList = pHead2;
            diff = len2 - len1;
        }

        //长链表先走diff 步
        for (int i = 0; i < diff; i++) {
            longList = longList.next;
        }

        //长短链表在不为空的情况下比较值大小
        while (longList != null && shortList != null && longList.val != shortList.val) {
            longList = longList.next;
            shortList = shortList.next;
        }

        return shortList;
    }
}