【leetcode】【单链表】【86】Partition List

#include<iostream>
using namespace std;

struct ListNode {
	int val;
	ListNode *next;
	ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
	ListNode* partition(ListNode* head, int x) {
		if (head == NULL || head->next == NULL)
			return head;
		ListNode* cur = head;
		ListNode* last = head;
		while (cur){//寻找第一个小于x的节点
			if (cur->val >= x){
				last = cur;//记录最后一个大于等于x的节点
				cur = cur->next;
			}
			else
				break;
		}
		if (cur == NULL) //所有节点的值都大于等于x
			return head;

		ListNode* first = head;//插入点的前一点
		head = cur;//第一个小于x的节点就是头结点

		if (head != first){//说明第一个小于x的节点前面有节点大于等于x
			last->next = head->next;
			head->next = first;
		}
		first = head;//插入点的前一点
		cur = last->next;
		while (cur){ //我用的方法是一个节点一个节点的插入，而没有用小于x的[first,last）内的节点整体插入
			if (cur->val < x){
				if (first==last){//前面的节点的值都是小于x
					first = last = cur;
					cur = cur->next;
				}else{ //有节点的值大于等于x
					last->next = cur->next;
					cur->next = first->next;
					first->next = cur;
					first = cur;
					cur = last->next;
				}
			}else{
				cur = cur->next;
				last = last->next;
			}
		}
		return head;
	}
	ListNode* createList(ListNode* head){
		int numOfNode;
		int value;
		cout << "please input number of listNode:";
		cin >> numOfNode;
		cin >> value;
		head = new ListNode(value);
		ListNode* cur = head;
		for (int i = 1; i < numOfNode; ++i){
			cin >> value;
			ListNode* temp = new ListNode(value);
			cur->next = temp;
			cur = temp;
		}
		return head;
	}
	void printNode(ListNode* head){
		ListNode* cur = head;
		while (cur){
			cout << cur->val << " ";
			cur = cur->next;
		}
		cout << endl;
	}
};

int main(){
	ListNode* head = NULL;
	Solution lst;
	head = lst.createList(head);
	lst.printNode(head);

	head = lst.partition(head, 4);
	lst.printNode(head);

	system("pause");
	return 0;
}