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practicalFive.cpp
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practicalFive.cpp
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/*
Construct an expression tree from the given prefix expression eg. +--a*bc/def and
traverse it using postordertraversal(non recursive) and then delete the entire tree.
*/
#include "bits/stdc++.h"
using namespace std;
class TreeNode {
public:
char data;
TreeNode *left, *right;
};
class ExpTree {
public:
TreeNode *top;
void getExpression(string);
void iterativePostOrder(TreeNode*);
void postOrder(TreeNode*);
void remove(TreeNode*);
};
void ExpTree::getExpression(string prefix) {
stack<TreeNode*> stk;
TreeNode *t1, *t2;
int len = prefix.size(), i;
for(i = len - 1; i >= 0; i--) {
top = new TreeNode;
top->left = top->right = nullptr;
if(isalpha(prefix[i])) {
top->data = prefix[i];
stk.push(top);
}else if(prefix[i] == '+' or prefix[i] == '*' or prefix[i] == '-' or prefix[i] == '/') {
t2 = stk.top();
stk.pop();
t1 = stk.top();
stk.pop();
top->data = prefix[i];
top->left = t2;
top->right = t1;
stk.push(top);
}
}
top = stk.top();
stk.pop();
}
void ExpTree::postOrder(TreeNode *root) {
if(root) {
postOrder(root->left);
postOrder(root->right);
cout << root->data;
}
}
void ExpTree::iterativePostOrder(TreeNode *root) {
if (root == nullptr) return;
stack<TreeNode*> stk;
stk.push(root);
TreeNode* prev = nullptr;
while (!stk.empty()) {
TreeNode* curr = stk.top();
if (!prev || prev->left == curr || prev->right == curr) {
if (curr->left) {
stk.push(curr->left);
} else if (curr->right) {
stk.push(curr->right);
} else {
cout << curr->data;
stk.pop();
}
} else if (curr->left == prev) {
if (curr->right) {
stk.push(curr->right);
} else {
cout << curr->data;
stk.pop();
}
} else if (curr->right == prev) {
cout << curr->data;
stk.pop();
}
prev = curr;
}
}
void ExpTree::remove(TreeNode *node) {
if(!node) return;
remove(node->left);
remove(node->right);
cout << "Removing node: " << node->data << endl;
delete node;
}
int main() {
ExpTree t;
string expr;
int ch = 0;
do {
cout << "Choose Options" << endl;
cout << "1. Input Expression " << endl;
cout << "2. Iterative & Recursive PostOrder " << endl;
cout << "3. Remove Nodes " << endl;
cout << "4. Exit" << endl;
cin >> ch;
switch(ch) {
case 1:
[&](){
cout << "Enter the prefix expression : ";
cin >> expr;
t.getExpression(expr);
}();
break;
case 2:
[&](){
cout << "Iterative Post Order" << endl;
t.iterativePostOrder(t.top);
cout << endl;
cout << "Recursive Post Order" << endl;
t.postOrder(t.top);
cout << endl;
}();
break;
case 3:
[&](){
cout << " Removing Elements " << endl;
t.remove(t.top);
}();
break;
}
}while(ch != 4);
}
/*
--------------------------------------------------------------------------------
OUTPUT
---------------------------------------------------------------------------------
Choose Options
1. Input Expression
2. Iterative & Recursive PostOrder
3. Remove Nodes
4. Exit
1
Enter the prefix expression : +--a*bc/def
Choose Options
1. Input Expression
2. Iterative & Recursive PostOrder
3. Remove Nodes
4. Exit
2
Iterative Post Order
abc*-de/-f+
Recursive Post Order
abc*-de/-f+
Choose Options
1. Input Expression
2. Iterative & Recursive PostOrder
3. Remove Nodes
4. Exit
3
Removing Elements
Removing node: a
Removing node: b
Removing node: c
Removing node: *
Removing node: -
Removing node: d
Removing node: e
Removing node: /
Removing node: -
Removing node: f
Removing node: +
Choose Options
1. Input Expression
2. Iterative & Recursive PostOrder
3. Remove Nodes
4. Exit
4
*/