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 ) {
    // write code here
    if (!head || !head.next){
        return false;
    }
    let slow = head;
    let fast = head.next;
    while(slow !== fast){
        if(!fast || !fast.next ){
            return false;
        }
        slow = slow.next;
        fast = fast.next.next;
    }
    return true;
}
module.exports = {
    hasCycle : hasCycle
};