面试过程中手撕代码之二叉树

二叉树的个人总结

由于本人目前在找算法工程师方向的工作，在面试过程中，经常会被问到非递归方法遍历的二叉树，二叉搜索树，二叉树的高度等一系列方法，本人写了c++代码供自己复习使用，希望也能够帮到各位小伙伴们

代码块

////  tree.cpp//  myTest////  Created by lixiaoxue on 2017/8/28.//  Copyright © 2017年 lixiaoxue. All rights reserved.//#include <stdio.h>#include <iostream>#include <queue>#include <vector>#include <algorithm>#include <math.h>#include <numeric>#include <stack>using namespace std;struct TreeNode{public:    int val;    TreeNode* left;    TreeNode* right;    TreeNode(int a): val(a),left(nullptr),right(nullptr){}};//递归先序遍历void pre_order(vector<int>& out,TreeNode* root){    if(!root) return;    out.push_back(root->val);    pre_order(out, root->left);    pre_order(out, root->right);}//递归中序遍历void mid_order(vector<int>& out,TreeNode* root){    if(!root) return;    mid_order(out, root->left);    out.push_back(root->val);    mid_order(out, root->right);}//递归的后序遍历void after_order(vector<int>& out,TreeNode* root){    if(!root) return;    after_order(out, root->left);    after_order(out, root->right);    out.push_back(root->val);}//非递归先序遍历2vector<int> pre_order_non2(TreeNode* root){    if(!root) return vector<int>();    vector<int> number;    stack<TreeNode*> s;    TreeNode* cur = root;    while ((!s.empty()) || !cur) {        while (cur) {            number.push_back(cur->val);            s.push(cur);            cur = cur->left;        }        if(!s.empty()){            cur = s.top()->right;            s.pop();        }    }    return number;}//先序遍历3vector<int> pre_order_non3(TreeNode* root){    if(!root) return vector<int>();    stack<TreeNode*> s;    vector<int> number;    while (root) {        number.push_back(root->val);        s.push(root);        root = root->left;    }    while (!s.empty()) {        TreeNode* temp = s.top()->right;        s.pop();        while (temp) {            number.push_back(temp->val);            s.push(temp);            temp = temp->left;        }    }    return number;}//中序遍历非递归vector<int> mid_order_non(TreeNode* root){    if(!root) return vector<int>();    stack<TreeNode*> s;    vector<int> number;    TreeNode* cur = root;    while ((!s.empty()) || cur) {        while (cur) {            s.push(cur);            cur = cur->left;        }        if (!s.empty()) {            TreeNode* temp = s.top();            s.pop();            number.push_back(temp->val);            cur = temp->right;        }    }    return number;}//中序遍历2vector<int> mid_order_non2(TreeNode* root){    if(!root) return vector<int>();    stack<TreeNode*> s;    vector<int> number;    TreeNode* cur = root->left;    while ((!s.empty())||cur) {        while (cur) {            s.push(cur);            cur = cur->left;        }        cur = s.top();        s.pop();        number.push_back(cur->val);        cur = cur->right;    }    return number;}//后序遍历vector<int> after_order_non(TreeNode* root){    if(!root) return vector<int>();    vector<int> number;    stack<TreeNode*> s;    TreeNode* cur = root;    TreeNode* last = nullptr;    while ((!s.empty()) || cur) {        while (cur) {            s.push(cur);            cur = cur->left;        }        cur = s.top();        if((!cur->right) || cur->right == last){            number.push_back(cur -> val);            last = cur;            s.pop();            cur = s.top();        }else            cur = cur->right;    }    return number;}void PostOrder_Nonrecursive(TreeNode* root)  // 后序遍历的非递归     双栈法{    stack<TreeNode*> s1 , s2;    TreeNode* curr ;           // 指向当前要检查的节点    s1.push(root);    while(!s1.empty())  // 栈空时结束    {        curr = s1.top();        s1.pop();        s2.push(curr);        if(curr->left)            s1.push(curr->left);        if(curr->right)            s1.push(curr->right);    }    while(!s2.empty())    {        printf("%c ", s2.top()->val);        s2.pop();    }}//求二叉树非遍历情况下的平均深度int findDepth(TreeNode* root){    if(!root) return 0;    root->val = 1;    vector<int> height;    vector<TreeNode*> tree{root};    while (tree.size()) {        root = tree.back();        tree.pop_back();        if(!root->left && !root->right)            height.push_back(root->val);        if(root->left){            tree.push_back(root->left);            root->left->val = root->val+1;        }        if(root->right){            tree.push_back(root->right);            root->right->val = root->val + 1;        }    }    int sum = accumulate(height.begin(), height.end(), 0);    cout << sum << "  " << height.size() << endl;    return (float)sum/(float)height.size();}//求二叉树非遍历情况下的平均深度int tree_depth(TreeNode* root){    if(!root) return 0;    vector<TreeNode*> temp{root};    int h =0;    vector<int> height;    while (temp.size()) {        h+= 1;        vector<TreeNode*> nei;        for(TreeNode* it:temp){            if(!it->left && !it->right)            {height.push_back(h);continue;}            if(it->left)                nei.push_back(it->left);            if (it->right) {                nei.push_back(it->right);            }        }        temp = nei;    }    int sum= accumulate(height.begin(), height.end(), 0);    cout << sum << " " << height.size() << endl;    return sum/height.size();}int main(){    TreeNode* root = new TreeNode(6);    TreeNode* left1 = new TreeNode(6);    TreeNode* right1 = new TreeNode(6);    TreeNode* left12 = new TreeNode(6);    TreeNode* left123 = new TreeNode(6);    TreeNode* left1234 = new TreeNode(6);    root->left = left1;    left1->left = left12;    left12->left = left123;    left123->right = left1234;    root->right = right1;    int zhi = tree_depth(root);    cout << zhi << endl;    return 0;}