判斷連結串列是否有環，並返回連結串列的第一個節點
阿新 • • 發佈：2018-12-26
class Solution {
private static ListNode function(ListNode head) {
if (head == null || head.next == null || head.next.next == null) {
return null;
}
ListNode slow = head.next;
ListNode fast = head.next.next;
while (slow != fast) {
slow = slow.next;
if (fast.next == null || fast.next.next == null) {
return null;
}
fast = fast.next.next;
}
fast = head;
while (slow != fast) {
slow = slow.next;
fast = fast.next;
}
return fast;
}
private static void print(ListNode head) {
while (head != null) {
System.out.println(head.val);
head = head.next;
}
}
private static void printEle(ListNode node) {
if (node == null) {
System.out.println("null");
} else {
System.out.println(node.val);
}
}
public static void main(String[] args) {
ListNode n1 = new ListNode(1);
ListNode n2 = new ListNode(2);
ListNode n3 = new ListNode(3);
ListNode n4 = new ListNode(4);
ListNode n5 = new ListNode(5);
n1.next = n2;
n2.next = n3;
n3.next = n4;
n4.next = n5;
// n5.next = n2;
ListNode head = function(n1);
printEle(head);
// print(head);
}
}
class ListNode {
int val;
ListNode next;
ListNode(int x) { val = x; }
}