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package class030 ;
// 测试链接：
public class Code04_EnterLoopNode {
// 这个类不用提交
public static class ListNode {
public int val ;
public ListNode next ;
}
// 只提交以下的代码
public static ListNode detectCycle ( 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 ) {
if ( fast . next = = null | | fast . next . next = = null ) {
return null ;
}
fast = fast . next . next ;
slow = slow . next ;
}
fast = head ;
while ( slow ! = fast ) {
slow = slow . next ;
fast = fast . next ;
}
return slow ;
}
}
