二叉树的三种遍历六种实现

#include <iostream> #include <stack>using namespace std;struct TreeNode {    int val;    struct TreeNode *left;    struct TreeNode *right;    TreeNode(int x) :            val(x), left(NULL), right(NULL) {    }};/**    TreeNode* init_node(int value);*/ TreeNode* init_node(){    TreeNode* r0 = new TreeNode(0);    TreeNode* r1 = new TreeNode(1);    TreeNode* r2 = new TreeNode(2);    TreeNode* r3 = new TreeNode(3);    TreeNode* r4 = new TreeNode(4);    TreeNode* r5 = new TreeNode(5);    TreeNode* r6 = new TreeNode(6);    r0->left = r1;r0->right = r2;    r1->left = r3;r1->right = r4;    r2->left = r5;r2->right = r6;    r3->left=r3->right=r4->left=r4->right=r5->left=r5->right=r6->left=r6->right=NULL;    return r0;}//前序遍历-递归实现 void pre_order0(TreeNode* root){    if(root == NULL)    return;    cout<<root->val<<'\t';    pre_order0( root->left);    pre_order0( root->right);}  //前序遍历-非递归实现 void pre_order(TreeNode* root){    if(root == NULL) return;     stack<TreeNode*> nodes;    TreeNode* tmp = root;    while(tmp != NULL){        cout<< tmp->val<<'\t';        if(tmp->right) nodes.push(tmp->right);        if(tmp->left) nodes.push(tmp->left);        if(nodes.empty())   break;        tmp = nodes.top();        nodes.pop();    }} //中序遍历-递归实现 void in_order(TreeNode* root){    if(root == NULL)    return;    in_order( root->left);    cout<<root->val<<'\t';    in_order(root->right);} //中序遍历-非递归实现void in_order_0(TreeNode* root){    stack<TreeNode*> nodes;    TreeNode* tmp = root;    while(!nodes.empty() || tmp){        if(tmp){            nodes.push(tmp);            tmp = tmp->left;         }else{            tmp = nodes.top();            cout<<tmp->val<<'\t';            nodes.pop();            tmp = tmp->right;         }    }}//后序遍历-递归实现void post_order(TreeNode* root){    if(root == NULL)    return;    post_order(root->left);    post_order(root->right);        cout<<root->val<<'\t';} //后序遍历-非递归实现void post_order0(TreeNode* root){    stack<TreeNode*> s;    TreeNode* h = root;    if(root == NULL)        return;    s.push(root);    while(!s.empty()){       TreeNode* cur = s.top();        if(cur->left != NULL && h != cur->left &&　h != cur->right)            s.push(cur->left);        else if(cur->right != NULL && h != cur->right){            s.push(cur->right);        }else{            cout<<cur->val<<'\t';            s.pop();            h = cur;        }    }}int main(){    TreeNode* root = init_node();    in_order_0(root);    return 0;}