Prove safety offer 17: merging two ordered lists

　　

Title Description

Two monotonically increasing input list and output list after synthesis of two lists, of course, after that we need to meet synthesis list - decreasing the rules.

 

Problem-solving ideas

Basic Operation inspection list, difficult to grasp that the input data, the input data must consider the comprehensive

1. When a single linked list is NULL;

2. The two lists are NULL;

3. A list traversal is completed, the remaining nodes as well as other chain

4. The two lists of equal length;

The following C ++ code realization are given specifically:

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        //边界检查
        if(pHead1==NULL){
            return pHead2;
        }
        if(pHead2==NULL){
            return pHead1;
        }
        ListNode *p1=pHead1,*p2=pHead2,*nHead=NULL;
        ListNode = Q * NULL;
         // determining first node fused 
        IF (P1-> Val <= P2-> Val) { 
            Q = P1; 
            P1 = P1-> Next; 
        } the else { 
            Q = P2; 
            P2 = P2- > Next; 
        } 
        NHEAD = Q;
         // set two pointers pointing to two lists, one by one to take a new list element is connected to 
        the while (P1 = P2 = NULL &&!! {NULL)
             IF (P1-> Val <= P2 -> Val) { 
                Q -> Next = P1; 
                P1 = P1-> Next;
                q=q->next;
                
            }else{
                q->next=p2;
                p2=p2->next;
                q=q->next;
            }
            
        }
        if(p1==NULL){
            q->next=p2;
        }else{
            q->next=p1;
        }       
        return nHead;
    }
};