题解 | #判断链表中是否有环#

快慢指针，干就完事了

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

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