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) {
        if(pHead1 == null || pHead2 == null) return null;

        int diff = diff(pHead1, pHead2);
        if(diff > 0) {
            while(diff > 0) {
                pHead1 = pHead1.next;
                diff--;
            }
        } else {
            while(diff < 0) {
                pHead2 = pHead2.next;
                diff++;
            }
        }
        while(pHead1 != null && pHead2 != null) {
            if(pHead1 == pHead2) return pHead1;
            pHead1 = pHead1.next;
            pHead2 = pHead2.next;
        }
        return null;

    }

    private int diff(ListNode l1, ListNode l2) {
        int length1 = 0;
        int length2 = 0;
        while(l1.next != null) {
            length1++;
            l1 = l1.next;
        }
        while(l2.next != null) {
            length2++;
            l2 = l2.next;
        }
        return length1 - length2;
    }
}