DAY 25 Binary tree preorder trevasrsal.cpp

// Problem 1 binary tree perorder trevarsal .cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *l;
 *     TreeNode *r;
 *     TreeNode() : val(0), l(nullptr), r(nullptr) {}
 *     TreeNode(int x) : val(x), l(nullptr), r(nullptr) {}
 *     TreeNode(int x, TreeNode *l, TreeNode *r) : val(x), l(l), r(r) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        stack<TreeNode*>st;// stack imput 
        TreeNode* node=root;
        vector<int> inorder; // vector 
 
        while(true)
        {
if(node!=NULL)
{
st.push(node);
node=node->left;
}
        else
        {
        if(st.empty() == true)
            break;
            node=st.top();
            st.pop();
            inorder.push_back(node->val);
            node=node->right;
            
        }}
return inorder;
    }
};

//problem 2Binary Tree Inorder Traversal.cpp
//
class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
       vector<int>preorder;
           if(root==NULL)
        return preorder;
        stack<TreeNode*>st;
        st.push(root);
        while(!st.empty())
        {
root=st.top();
        st.pop();
        preorder.push_back(root->val);
        if(root->right!=NULL)
        {
        st.push(root->right);
        }
if(root->left!=NULL)
{
    st.push(root->left);
}
}return preorder;       
    }
};


//problem 3 Binary Tree postorder Traversal

class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
       vector<int>postorder;
        if(root ==NULL)
            return postorder;
        stack<TreeNode* >s1,s2;
        s1.push(root);
        while(!s1.empty())
        {
    root=s1.top();
            s1.pop();
            s2.push(root);
            if(root->left!=NULL)
                s1.push(root->left);
            if(root->right!=NULL)
                s1.push(root->right);
        }
        while(!s2.empty())
        {
            postorder.push_back(s2.top()->val);
            s2.pop();
        }
        return postorder;
        }
};