在单链表中的特定节点之前插入节点

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def insertNodeBefore(target_node, new_node_val):
    # 创建新节点
    new_node = ListNode(new_node_val)
    
    # 遍历链表，找到目标节点的前一个节点
    curr = head
    while curr.next != target_node:
        curr = curr.next
    
    # 插入新节点
    new_node.next = target_node
    curr.next = new_node

# 示例用法
# 创建链表：1 -> 2 -> 3 -> 4
head = ListNode(1)
node2 = ListNode(2)
node3 = ListNode(3)
node4 = ListNode(4)
head.next = node2
node2.next = node3
node3.next = node4

# 在节点2之前插入新节点5
insertNodeBefore(node2, 5)