剑指67/JZ55链表中环的入口结点.html

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    <meta charset="UTF-8" />
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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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    <script>
      // 给一个链表，若其中包含环，请找出该链表的环的入口结点，否则，输出null。

      function ListNode(x) {
        this.val = x;
        this.next = null;
      }
      function EntryNodeOfLoop(pHead) {
        // write code here
        if (!pHead) return null;
        let p = pHead;
        let hash = new Map();
        while (p) {
          if (hash.has(p)) {
            return p;
          } else {
            hash.set(p, true);
          }
          p = p.next;
        }

        return null;
      }

      // 慢快指针， 有环的话 快一定会等于(追上)慢
      var hasCycle = function (head) {
        if (!head || !head.next) return false;
        let slow = head;
        let fast = head.next;
        while (fast != slow) {
          if (!fast || !fast.next) return false;
          slow = slow.next;
          fast = fast.next.next;
        }
        return fast;
      };

      const A = new ListNode('A');
      const B = new ListNode('B');
      const C = new ListNode('C');
      const D = new ListNode('D');

      A.next = B;
      B.next = C;
      C.next = D;
      D.next = B;

      const a = new ListNode('a');
      const b = new ListNode('b');
      const c = new ListNode('c');
      const d = new ListNode('d');

      a.next = b;
      b.next = c;
      c.next = d;

      console.log('EntryNodeOfLoop A = ', EntryNodeOfLoop(A));
      console.log('EntryNodeOfLoop a = ', EntryNodeOfLoop(a));
    </script>
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</html>