史上最全二叉树的遍历方法

#include<iostream>#include<sstream>#include<set>#include<stack>#include<queue>#include<vector>using namespace std;namespace tree{struct TNode {    TNode* left;    TNode* right;    int val;    TNode(int val):left(nullptr),right(nullptr),val(val){}};/** * 先序遍历二叉树 **/void pre_order(TNode* root) {    if (root == nullptr) return;    cout<<root->val<<",";    pre_order(root->left);    pre_order(root->right);}/** * 中序遍历二叉树 **/void in_order(TNode* root) {    if(root == nullptr) return;    in_order(root->left);    cout<<root->val<<",";    in_order(root->right);}/** * 后序遍历二叉树 **/void post_order(TNode* root) {    if (root == nullptr) return;    post_order(root->left);    post_order(root->right);    cout<<root->val<<",";}/** * 层序遍历 **/void level_order_visit(vector<TNode*> q) {    if (q.empty()) return;    vector<TNode*> qNext;    for (auto ele : q) {        cout<<ele->val<<",";        if (ele->left) {            qNext.push_back(ele->left);        }        if (ele->right) {            qNext.push_back(ele->right);        }    }    level_order_visit(qNext);}/** * 层序遍历迭代版，支持分层打包 **/void level_order_visit_iter(TNode* root) {    queue<TNode*> q;    q.push(root);    q.push(nullptr);    while (!q.empty()) {        auto cur = q.front();        q.pop();        if (cur == nullptr) {            if (q.empty() == false) q.push(nullptr);        } else {            cout<<cur->val<<",";            if (cur->left) {                q.push(cur->left);            }            if (cur->right) {                q.push(cur->right);            }        }    }    cout<<endl;}void level_order_visit_iter_II(TNode* root) {    set<TNode*> visited;    queue<TNode*> q;    q.push(root);    while(!q.empty()) {        TNode* tmp = q.front();        cout<<tmp->val<<",";        q.pop();        if (tmp->left) {            q.push(tmp->left);        }        if (tmp->right) {            q.push(tmp->right);        }    }}void in_order_iter(TNode* root) {    stack<TNode*> s;    TNode* cur = root;    while(!s.empty() || cur != nullptr) {        while(cur != nullptr) {            s.push(cur);            cur = cur->left;        }        TNode* tmp = s.top();        cout<<tmp->val<<",";        s.pop();        cur = tmp->right;    }}void pre_order_iter(TNode* root) {    stack<TNode*> s;    TNode* cur = root;    while(!s.empty() || cur != nullptr) {        while(cur != nullptr) {            s.push(cur);            cout<<cur->val<<",";            cur = cur->left;        }        TNode* tmp = s.top();        s.pop();        cur = tmp->right;    }}void post_order_iter(TNode* root) {    stack<TNode*> s;    TNode* cur = root;    TNode* pre = nullptr;    while (!s.empty() || cur != nullptr) {        while (cur != nullptr) {            s.push(cur);            cur = cur->left;        }        TNode* tmp = s.top();        if (tmp->right == pre || tmp->right == nullptr) {            cout<<tmp->val<<",";            pre = tmp;            s.pop();            cur = nullptr;        } else {            cur = tmp->right; //写错的原因是思路不清晰        }    }}/** * morris 先序遍历算法 **/void morris_pre_order(TNode* root) {    TNode* cur = root;    while(cur) {        if (cur->left == nullptr) {            cout<<cur->val<<",";            cur = cur->right;            return;        }        TNode* curInner = cur->left;        while (curInner->right != nullptr && curInner->right != cur) {            curInner = curInner->right;        }        if(curInner->right == nullptr) {            curInner->right = cur;            cur = cur->left;            cout<<cur->val<<",";        } else {            curInner->right = nullptr;            cur = cur->right;        }    }}/** * morris 中序遍历算法 **/void morris_in_order(TNode* root) {    TNode* cur = root;    while(cur) {        if (cur->left == nullptr) {            cout<<cur->val<<",";            cur = cur->right;            return;        }        TNode* curInner = cur->left;        while (curInner->right != nullptr && curInner->right != cur) {            curInner = curInner->right;        }        if(curInner->right == nullptr) {            curInner->right = cur;            cur = cur->left;        } else {            curInner->right = nullptr;            cout<<cur->val<<",";            cur = cur->right;        }    }}/** * morris 后续遍历算法 **/void revert_link(TNode* beg, TNode* end) {    TNode* head = beg->right;    TNode* cur = beg;    while (cur != end) {        TNode* head_tmp = head->right;        head->right = cur;        cur = head;        head = head_tmp;    }    beg->right = nullptr;}void visit_link(TNode* beg, TNode* end) {    revert_link(beg, end);    TNode* cur = end;    while (cur != nullptr) {        cout<<cur->val<<",";        cur = cur->right;    }    revert_link(end, beg);}void morris_post_order(TNode* root) {    TNode* tmp_root = new TNode(0);    tmp_root->left = root;    TNode* cur = tmp_root;    while(cur != nullptr) {        if (cur->left == nullptr) {            cur = cur->right;            continue;        }        TNode* tmp = cur->left;        while (tmp->right != nullptr && tmp->right != cur) tmp = tmp->right;        if (tmp->right == nullptr) {            tmp->right = cur;            cur = cur->left;        } else {            tmp->right = nullptr;            TNode* beg = cur->left;            TNode* end = tmp;            visit_link(beg, end);            cur = cur->right;        }    }    delete tmp_root;    tmp_root = nullptr;}/** * 构建二叉树 **/int string2int(string& in) {    stringstream ss(in);    int ret;    ss>>ret;    return ret;}TNode* create_tree(vector<string>& tree) {    queue<TNode*> q;    TNode* root = new TNode(string2int(tree[0]));    q.push(root);    int cur_index = 1;    while (q.empty() == false) {        TNode* cur = q.front();        q.pop();        for (int i = 0; i < 2; ++i) {            if (cur_index < tree.size()) {                if (tree[cur_index] != "#") {                    int digit = string2int(tree[cur_index]);                    if (i == 0) {                         cur->left = new TNode(digit);                         q.push(cur->left);                    } else {                         cur->right = new TNode(digit);                         q.push(cur->right);                    }                }                 cur_index += 1;            }        }    }    return root;}}int main() {    int n = 0;    cin>>n;    vector<string> tree;    for (int i = 0; i < n; ++i) {        string s;        cin>>s;        tree.push_back(s);    }    tree::TNode* root = tree::create_tree(tree);    tree::pre_order(root);        cout<<endl;    tree::pre_order_iter(root);        cout<<endl;    tree::post_order(root);        cout<<endl;    tree::post_order_iter(root);        cout<<endl;    tree::in_order(root);    cout<<endl;    tree::in_order_iter(root);    cout<<endl;    vector<tree::TNode*> root_vec;    root_vec.push_back(root);    tree::level_order_visit(root_vec);    cout<<endl;    tree::level_order_visit_iter(root);    cout<<endl;    return 0;}