题解 | #判断链表中是否有环#

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
 * 
 * @param head ListNode类 
 * @return bool布尔型
 */
function hasCycle( head ) {
  let fast = head,
      slow = head
  
  if (fast === null || fast.next === null || fast.next.next === null) {
    return false
  }
  while (fast && fast.next) {
    slow = slow.next
    fast = fast.next.next
    
    if (slow === fast) {
      return true
    }
  }
  
  return false
}
module.exports = {
    hasCycle : hasCycle
};