[LeetCode] 86. Partition List 划分链表
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
给一个链表和一个x值，划分链表，把所有小于x值的节点都移到大于等于x值的前面，两部分的节点顺序不变。
解法：维护两个queue，一个存小于x值的，一个存大于等于x值的，最后在把两个连在一起。记得把大于等于的最后加上null。
Java:
public ListNode partition(ListNode head, int x) {
ListNode dummy1 = new ListNode(0), dummy2 = new ListNode(0); //dummy heads of the 1st and 2nd queues
ListNode curr1 = dummy1, curr2 = dummy2; //current tails of the two queues;
while (head!=null){
if (head.val<x) {
curr1.next = head;
curr1 = head;
}else {
curr2.next = head;
curr2 = head;
}
head = head.next;
}
curr2.next = null; //important! avoid cycle in linked list. otherwise u will get TLE.
curr1.next = dummy2.next;
return dummy1.next;
}
Python:
# Time: O(n)
# Space: O(1)
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
def __repr__(self):
if self:
return "{} -> {}".format(self.val, repr(self.next))
class Solution(object):
# @param head, a ListNode
# @param x, an integer
# @return a ListNode
def partition(self, head, x):
dummySmaller, dummyGreater = ListNode(-1), ListNode(-1)
smaller, greater = dummySmaller, dummyGreater
while head:
if head.val < x:
smaller.next = head
smaller = smaller.next
else:
greater.next = head
greater = greater.next
head = head.next
smaller.next = dummyGreater.next
greater.next = None
return dummySmaller.next
C++:
// Time: O(n)
// Space: O(1)
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *partition(ListNode *head, int x) {
ListNode dummy_smaller{0};
ListNode dummy_larger{0};
auto smaller = &dummy_smaller;
auto larger = &dummy_larger;
while (head) {
if (head->val < x) {
smaller->next = head;
smaller = smaller->next;
} else {
larger->next = head;
larger = larger->next;
}
head = head->next;
}
smaller->next = dummy_larger.next;
larger->next = nullptr;
return dummy_smaller.next;
}
};
C++:
ListNode *partition(ListNode *head, int x) {
ListNode node1(0), node2(0);
ListNode *p1 = &node1, *p2 = &node2;
while (head) {
if (head->val < x)
p1 = p1->next = head;
else
p2 = p2->next = head;
head = head->next;
}
p2->next = NULL;
p1->next = node2.next;
return node1.next;
}
