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86. Partition List

Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

Example:
Input: head = 1->4->3->2->5->2, x = 3
Output: 1->2->2->4->3->5

思路分析

思路很简单,直接双指针维护大小两个队列就好。

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  • 一刷

  • 二刷

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/**
 * Runtime: 0 ms, faster than 100.00% of Java online submissions for Partition List.
 * Memory Usage: 37.5 MB, less than 5.77% of Java online submissions for Partition List.
 *
 * @author D瓜哥 · https://www.diguage.com
 * @since 2020-02-05 19:14
 */
public ListNode partition(ListNode head, int x) {
    if (Objects.isNull(head)) {
        return null;
    }
    ListNode dummySmall = new ListNode(0);
    ListNode dummyLarge = new ListNode(0);
    ListNode tailSmall = dummySmall;
    ListNode tailLarge = dummyLarge;
    while (Objects.nonNull(head)) {
        if (head.val < x) {
            tailSmall.next = head;
            tailSmall = tailSmall.next;
        } else {
            tailLarge.next = head;
            tailLarge = tailLarge.next;
        }
        head = head.next;
    }
    tailLarge.next = null;
    tailSmall.next = dummyLarge.next;

    return dummySmall.next;
}
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/**
 * @author D瓜哥 · https://www.diguage.com
 * @since 2024-09-14 16:17:29
 */
public ListNode partition(ListNode head, int x) {
  ListNode small = new ListNode();
  ListNode smallTail = small;
  ListNode big = new ListNode();
  ListNode bigTail = big;

  while (head != null) {
    if (head.val < x) {
      smallTail.next = head;
      smallTail = smallTail.next;
    } else {
      bigTail.next = head;
      bigTail = bigTail.next;
    }
    head = head.next;
  }
  smallTail.next = big.next;
  bigTail.next = null;
  return small.next;
}

参考资料