java 代码

class Solution {
    public ListNode findFirstCommonNode(ListNode headA, ListNode headB) {
        Stack<ListNode> a = new Stack();
        Stack<ListNode> b = new Stack();
        while(headA!=null || headB!=null){
            if(headA!=null) {
                a.push(headA);
                headA = headA.next;
            }
            if(headB!=null){
                b.push(headB);
                headB = headB.next;  
            }
        }
        ListNode tmp = null;
        while(!a.isEmpty() && !b.isEmpty()){
            ListNode f = a.pop();
            ListNode s = b.pop();
            if(f==s){
                tmp = f;
            }else{
                break;
            }
        }
        return tmp;
    }
}

a+c+b b+c+a

class Solution {
    public ListNode findFirstCommonNode(ListNode headA, ListNode headB) {
        ListNode p = headA;
        ListNode q = headB;
        while(p != q){
            if(p!=null) p = p.next;
            else p = headB;
            if(q!=null) q = q.next;
            else q = headA;
        }
        return p;
    }
}