[leetcode] Partition List

Partition List

分成两个链表，一个比x小，一个比x大，然后再拼接。

#include "iostream"
using namespace std;

/**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) {
        
        if (head==NULL) {
            return NULL;
        }
        
        //cout<<head->val<<endl;
        
        ListNode *small=new ListNode(0);
        ListNode *big=new ListNode(0);
        ListNode *p=small;
        ListNode *q=big;
        ListNode *current=head;
        
        //cout<<current->val<<endl;
        
        while (current!=NULL) {
            if (current->val<x) {
                p->next=current;
                current=current->next;//切记，不能使用current++！！！
                p=p->next;
            }else{
                q->next=current;
                current=current->next;
                q=q->next;
            }
        }
        
        if (p==small||q==big) {//都比x大or小
            return head;
        }
        
        //连接两个串
        
        p->next=big->next;
        q->next=NULL;
        current=small->next;
        
        //记得释放内存
        free(small);
        free(big);
        
        return current;
        
        
    }
};


int main() {
    ListNode *t=new ListNode(1);
    t->next=new ListNode(2);
    cout<<t->val<<endl;
    Solution so;
    ListNode *res= so.partition(t, 2);
    cout<<res->val<<res->next->val<<endl;
    return 0;
}