Morris遍历以及Morris前序中序后序遍历实现

#include<iostream>
using namespace std;

struct TreeNode{
    int val;
    TreeNode* right;
    TreeNode* left;
    TreeNode(int _val):val(_val),right(nullptr),left(nullptr){}
};

void Morris(TreeNode* root){
     if(root == nullptr)
           return;
     TreeNode* cur=root;
     TreeNode* mostRight=nullptr;

    //当cur为空停止，即上图中的情况3
     while(cur != nullptr){
         mostRight=cur->left;
         //如果mostRight!=nullptr，进入情况2
         if(mostRight != nullptr){
              while(mostRight->right && mostRight != cur)
                      mostRight=mostRight->right; 
              //当mostRight == nullptr，即情况2.a
              if(mostRight->right == nullptr){
                      mostRight->right=cur;
                      cur=cur->left;
                      continue;
              }
              else{             //当mostRight == cur，即情况2.b
                    mostRight->right=nullptr;
                     /*cur=cur->left;
                     continue;*/
               }
         }
          //mostright为空进入情况1
          cur=cur->left;  
    }
}    

Morris前序遍历

有左子树就会回到cur节点两次，没有就来一次

void MorrisPre(TreeNode* root) {
    if (root == nullptr)
        return;
    TreeNode* cur = root;
    TreeNode* mostRight = nullptr;

    while (cur != nullptr) {
        mostRight = cur->left;

        if (mostRight != nullptr) {
            while (mostRight->right && mostRight->right != cur) {
                mostRight = mostRight->right;
            }

            if (mostRight->right == nullptr) {        
                //第一次到达左子树的最右子树
                printf("%d ", cur->val);
                mostRight->right = cur;
                cur = cur->left;
                continue;
            }
            else {                                    
                //第二次到达左子树的最右子树 
                mostRight->right == cur;
                mostRight->right = nullptr;
                /*cur = cur->right;
                continue;*/
            }
        }
        else {        
            //当前cur只能来一次
            printf("%d ", cur->val);
        }

        cur = cur->right;
    }
}

Morris中序遍历

void MorrisIn(TreeNode* root) {
    if (root == nullptr)
        return;
    TreeNode* cur = root;
    TreeNode* mostRight = nullptr;

    while (cur != nullptr) {
        mostRight = cur->left;

        if (mostRight != nullptr) {
            while (mostRight->right && mostRight->right != cur) {
                mostRight = mostRight->right;
            }

            if (mostRight->right == nullptr) {        //第一次到达左子树的最右子树
                mostRight->right = cur;
                cur = cur->left;
                continue;
            }
            else {                                    //第二次到达左子树的最右子树 mostRight->right == cur;
                mostRight->right = nullptr;
                /*cur = cur->right;
                continue;*/
            }
        }

        //往右移动的时候打印
        printf("%d ", cur->val);
        cur = cur->right;
    }
}

Morris后序遍历

//右孩子指向上一个节点
TreeNode* ReverseNode(TreeNode* node) {
    TreeNode* pre = nullptr;
    TreeNode* next = nullptr;
    while (node) {
        next = node->right;
        node->right = pre;
        pre = node;
        node = next;
    }
    return pre;
}

//逆序打印左孩子的右边界
void PrintNode(TreeNode* node) {
    TreeNode* tail = ReverseNode(node);
    TreeNode* cur = tail;
    while (cur) {
        printf("%d ", cur->val);
        cur = cur->right;
    }
    ReverseNode(tail);        //还原
}


void MorrisPos(TreeNode* root) {
    if (root == nullptr)
        return;
    TreeNode* cur = root;
    TreeNode* mostRight = nullptr;

    while (cur != nullptr) {
        mostRight = cur->left;

        if (mostRight != nullptr) {
            while (mostRight->right && mostRight->right != cur) {
                mostRight = mostRight->right;
            }

            if (mostRight->right == nullptr) {        //第一次到达左子树的最右子树
                mostRight->right = cur;
                cur = cur->left;
                continue;
            }
            else {                                    //第二次到达左子树的最右子树 mostRight->right == cur;
                mostRight->right = nullptr;

                //逆序打印左子树的右边界
                PrintNode(cur->left);
            }
        }
        cur = cur->right;
    }

    PrintNode(root);
}