二叉樹的非遞歸遍歷

#include <iostream>
#include <stack>

using namespace std;

class TreeNode{
public:
    TreeNode(int v){val = v;};
    int val;
    TreeNode* left;
    TreeNode* right;
};

void prevOrder(TreeNode* root){
    TreeNode* curr;
    stack<TreeNode*> s;
    curr = root;
    while(curr || !s.empty()){
        while(curr){
            cout<<curr->val<<endl;
            s.push(curr);
            curr = curr->left;
        }
        if(!s.empty()){
            curr = s.top();
            s.pop();
            curr = curr->right;
        }
    }
}

void postOrder(TreeNode* root){
    stack<TreeNode*> s;
    TreeNode* curr;
    TreeNode* lastPopedNode=NULL;
    s.push(root);
    while(!s.empty()){
        curr = s.top();
        TreeNode* lastChild = NULL;
        if(curr->left) lastChild = curr->left;
        if(curr->right) lastChild = curr->right;

        if(lastChild && lastPopedNode!=lastChild){
            if(curr->right) s.push(curr->right);
            if(curr->left) s.push(curr->left);
        }else{
            cout<<curr->val<<endl;
            s.pop();
            lastPopedNode = curr;
        }
    }
}

TreeNode* constructTree(int* A, int l ,int r){
    if(l>r) return NULL;
    int mid = (l+r)/2;
    TreeNode* root = new TreeNode(A[mid]);
    root->left = constructTree(A, l, mid-1);
    root->right = constructTree(A, mid+1, r);
}

int main(){
    int A[] = {1,2,3,4};
    int n = sizeof(A)/sizeof(int);
    TreeNode* root = constructTree(A, 0, n-1);
    postOrder(root);
    return 0;
}