[Programmer Interview Gold Code] Linked List Segmentation

Question 11 done by Nioke Online, title address: https://www.nowcoder.com/practice/0e27e0b064de4eacac178676ef9c9d70?tpId=8&tqId=11004&rp=1&ru=/ta/cracking-the-coding-interview&qru=/ta/cracking -the-coding-interview/question-ranking

Topic description:

Write code to split the linked list into two parts based on a given value x, and all nodes less than x are sorted before nodes greater than or equal to x. Given a linked list head pointer ListNode* pHead, return the head pointer of the rearranged linked list. Note: The original data order remains unchanged after splitting.

AC code, containing test data:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

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

class Partition {
public:
    ListNode* partition(ListNode* pHead, int x){
        ListNode* fkrt1 = new ListNode(0);
        ListNode* fkrt2 = new ListNode(0);

        ListNode* pSmall = fkrt1;
        ListNode* pGe = fkrt2;

        while(pHead!=NULL){
            if(pHead->val < x){
                pSmall->next = pHead;
                pSmall = pSmall->next;
            }else{
                pGe->next = pHead;
                pGe = pGe->next;
            }
            pHead = pHead->next;
        }

        pSmall->next = fkrt2->next;

        // 下面这行很容易漏掉。处理的是边界情况：最后一个大于阈值x的值，如果它不是链表末尾，
        // 那么在返回结果后进行遍历时，链表就没有终止了，产生环。显然应该避免环。
        pGe->next = NULL;
        
        ListNode* res = fkrt1->next;
        delete fkrt1;
        delete fkrt2;
        return res;
    }
};

int main() {
    //vector<int> vals = {1, 3, 5, 7, 9, 11, 2, 4, 6, 8, 10};
    vector<int> vals = {6,7,8,9,10,11, 1,2,3,4,5};
    vector<ListNode*> vl;
    for(int i=0; i<vals.size(); i++){
        vl.push_back(new ListNode(vals[i]));
        if(i>0){
            vl[i-1]->next = vl[i];
        }
    }
    cout << "the original datums are:" << endl;
    for(int i=0; i<vals.size(); i++){
        cout << vals[i] << ",";
    }
    cout << endl;

    ListNode* head = vl[0];
    Partition p;
    int x = 6;
    ListNode* res = p.partition(head, x);
    cout << "do splitting with thresh value = " << x << ", gains: " << endl;
    while(res!=NULL){
        cout << res->val << ",";
        res = res->next;
    }
    cout << endl;

    return 0;
}