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) {
	  //任意一条链表为空，就不会有公共节点
        if (pHead1 == null || pHead2 == null) {
            return null;
        }
        int c1 = 0;
        int c2 = 0;
        ListNode temp1 = pHead1;
        ListNode temp2 = pHead2;
	//公共部分等长，所以先保证从两链表等长的地方开始
        while (temp1 != null) {
            c1++;
            temp1 = temp1.next;
        }
        while (temp2 != null) {
            c2++;
            temp2 = temp2.next;
        }
        int diff = 0;
        if (c1 >= c2) {
            diff = c1 - c2;
            while (diff-->0) {
                pHead1 = pHead1.next;
            }
        } else {
            diff = c2 - c1;
            while (diff-->0) {
                pHead2 = pHead2.next;
            }
        }
	  //找公共节点
        while (pHead1 != null && pHead2 != null) {
            if (pHead1 == pHead2) {
                return pHead1;
            }
            pHead1 = pHead1.next;
            pHead2 = pHead2.next;
        }

        return null;
    }
}