2018-08-11 23:50:30
问题描述:
问题求解:
解法一、归并排序
public ListNode sortList(ListNode head) { if (head == null || head.next == null) return head; ListNode prev = null, slow = head, fast = head; while (fast != null && fast.next != null) { prev = slow; slow = slow.next; fast = fast.next.next; } prev.next = null; ListNode l1 = sortList(head); ListNode l2 = sortList(slow); return merge(l1, l2); } private ListNode merge(ListNode l1, ListNode l2) { ListNode dummy = new ListNode(0); ListNode p = dummy; while (l1 != null && l2 != null) { if (l1.val < l2.val) { p.next = l1; l1 = l1.next; } else { p.next = l2; l2 = l2.next; } p = p.next; } if (l1 != null) { p.next = l1; } if (l2 != null) { p.next = l2; } return dummy.next; }
解法二、快速排序
public ListNode sortList(ListNode head) { if (head == null || head.next == null) return head; qsort(head, null); return head; } // [begin, end) void qsort(ListNode begin, ListNode end) { if (begin == end || begin.next == end) return; ListNode mid = partition(begin, end); qsort(begin, mid); qsort(mid.next, end); } ListNode partition(ListNode begin, ListNode end) { int key = begin.val; ListNode p = begin; ListNode q = begin.next; while (q != end) { if (q.val < key) { p = p.next; int tmp = p.val; p.val = q.val; q.val = tmp; } q = q.next; } int tmp = p.val; p.val = begin.val; begin.val = tmp; return p; }