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Floyd.java
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65 lines (60 loc) · 1.17 KB
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public class Floyd {
/**
* Floyd判圈算法（双指针）
* @param head
* @return
*/
public boolean hasCycle(ListNode head){
if(head == null || head.next == null)
return false;
ListNode slow = head;
ListNode fast = head;
do{
if(fast == null || fast.next == null) return false;
slow = slow.next;
fast = fast.next.next;
}while(slow != fast);
return true;
}
/**
* 如果存在环，则求出环长
* @param head
* @return
*/
public int countCycleLength(ListNode head) {
if(!hasCycle(head)){
return 0;
}
ListNode slow = head;
ListNode fast = head;
do{
slow = slow.next;
fast = fast.next.next;
}while(slow != fast);
int cycleLength = 0;
do{
slow = slow.next;
fast = fast.next.next;
cycleLength++;
}while(slow != fast);
return cycleLength;
}
//找到环的起始位置
public ListNode detectCycle(ListNode head) {
if(!hasCycle(head)){
return null;
}
ListNode slow = head;
ListNode fast = head;
do{
slow = slow.next;
fast = fast.next.next;
}while(slow != fast);
ListNode start = head;
while(slow != start){
slow = slow.next;
start = start.next;
}
return start;
}
}