剑指offer中栈和树的总结

1.栈部分

#include<iostream>
using  namespace std;
struct listnode
{
	int val;
	listnode* next;
	listnode(int x) :val(x), next(nullptr) {}
};
 
listnode* listcreate() //创建
{   
	
	listnode * phead = new listnode(0);
	listnode * pcurrent = nullptr;
	pcurrent = phead;
	int data;
	while (cin>>data)
	{
		listnode* pnew = new listnode(data);
		pcurrent->next = pnew;
		pcurrent = pnew;
	}
	return phead->next;
}
 void printlist(listnode *phead)  //打印
{
	listnode * temp = nullptr;
	temp = phead;
	while (temp)
	{
		cout << temp->val;
		temp = temp->next;
	}
	delete temp;
}
 listnode* insertnode(listnode* phead,int x, int y) //插入y到x之后
 {
	 listnode * pcurrent = nullptr;
	 pcurrent = phead;
	 while (pcurrent->val!=x)
	 {
		 pcurrent = pcurrent->next;
	 }
	 listnode *pnew = new listnode(y);
	 pnew->next = pcurrent->next;
	 pcurrent->next = pnew;
	 return phead;
 }
 listnode *deleteData(listnode* phead,int data) //删除节点为data的节点
 {
	 listnode* pcurrent = nullptr;
	 listnode* prev = nullptr;
	 pcurrent = phead;
	 prev = phead;
	 while (pcurrent->val!=data&&pcurrent!=nullptr)
	 {  
		 prev = pcurrent;
		 pcurrent = pcurrent->next;
		 if (pcurrent == nullptr)
		 {
			 cout << " 无";
			 return phead;
		 }
	 }
	 
		 prev->next = pcurrent->next;
		 delete pcurrent;
	 
	
	 
	// delete prev; 这个prev不能删除= =
	 return phead;
 }
 int destroylist(listnode *phead)//销毁链表
 {
	 listnode *ptem = nullptr;
	 ptem = phead;
	 while (phead)
	 {
		 ptem = ptem->next;
		 delete phead;
		 phead = ptem;
	 }
	 return 0;
 }
 listnode* reverselist(listnode*phead)//翻转链表
 {
	 listnode* prev = nullptr;
	 listnode* pcurrent = nullptr; 
		 listnode* pnext = nullptr;
	 prev = phead;
	 pcurrent = prev->next;
	 
	 while (pcurrent)
	 {  
		 pnext = pcurrent->next;
		 pcurrent->next = prev;
		 prev = pcurrent;
		 pcurrent = pnext;
	 }
	 phead->next = nullptr;
	 return prev;

 }
 listnode* bottomKnode(listnode* phead,int k)//倒数第K个节点
 {  /*
	
		 listnode* p1 = phead;
	 listnode* p2 = phead;
	 int count = 0;
	 while (p1)
	 {
		 p1 = p1->next;
		 count++;
	 }
	 for (int i =1; i <=count-k; i++)
	 {
		 p2 = p2->next;
	 }
	*/
	 listnode* p1 = phead;
	 listnode* p2 = phead;
	 for (int i = 0; i < k-1; i++)
	 {
		 p1 = p1->next;
	 }
	 while (p1->next!=nullptr)
	 {
		 p1 = p1->next;
		 p2 = p2->next;
	 }
	 return p2;
 }
 listnode* merge(listnode*phead1, listnode*phead2)
 {
	 if (phead1==nullptr)
	 {
		 return phead2;
	 }
	 else
	 {
		 if (phead2==nullptr)
		 {
			 return phead1;
		 }
	 }   
	 listnode *mergenode=nullptr;
	 if (phead1->val>phead2->val)
	 {
		 mergenode = phead1;
		 mergenode->next = merge(phead1->next, phead2);
	 }
	 else
	 {
		 mergenode = phead2;
		 mergenode->next = merge(phead1, phead2->next);
	 }
	 return mergenode;
 }
 listnode* commonnode(listnode*phead1, listnode*phead2)//找出公共的第一个节点
 {
	 int len1 = getlistlen(phead1);
	 int len2 = getlistlen(phead2);
	 listnode*shortlist = nullptr;
	 listnode*longlist = nullptr;
	 listnode*commonnode = nullptr;
	 int step = 0;
	 if (len1>len2)
	 {
		 step = len1 - len2;
		 longlist = phead1;
		 shortlist = phead2;
	 }
	 else
	 {
		 step = len2 - len1;
		 longlist = phead2;
		 shortlist = phead1;
	 }
	 for (int i = 0; i < step; i++)
	 {
		 longlist = longlist->next;
	 }
	 while (longlist!=nullptr&&shortlist!=nullptr)
	 {  
		 longlist = longlist->next;
		 shortlist = shortlist->next;
		 if (longlist == shortlist)
		 {
			 commonnode = longlist;
			 break;
		 }
	 }
	 return commonnode;
	
 }
 int getlistlen(listnode *phead)
 {
	 listnode *temp = phead;
	 int len = 0;
	 while (temp)
	 {
		 temp = temp->next;
		 len++;
	 }
	 return len;
 }
 int main()
 {
	 //新建链表测试
	 
	 listnode* node = listcreate();
	 //打印链表测试
	 printlist(node);
	 cout << endl;

	 //插入链表测试
	  listnode* node5 = insertnode(node ,3,4);
	 printlist(node5);
	 cout << endl;

	 //删除链表测试
	 listnode* node6 = deleteData(node,6);
	 printlist(node6);
	 cout << endl;
	 //翻转链表测试
	 listnode* node7 = reverselist(node);
	 printlist(node7);
 }

2.树部分

1.二叉树的深度
结构

struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};

开始用DFS，爆栈
相当简洁的解法而且有动态规划内味

class Solution {
public:
    int TreeDepth(TreeNode* pRoot){
        if(!pRoot) return 0 ;
            return max(1+TreeDepth(pRoot->left), 1+TreeDepth(pRoot->right));
    }
};

2.二叉树的镜像
这道题算是写出来但是有个问题，不能把临时指针delete?

class Solution {
public:
    void Mirror(TreeNode *pRoot) {
        if (pRoot == nullptr)
        { return;}
        TreeNode* tmp=pRoot->left;
        pRoot->left=pRoot->right;
        pRoot->right=tmp;
        //delete tmp;错误 删除
        Mirror(pRoot->left);
        Mirror(pRoot->right);
        
    }
};