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syntax_tree_traversal.cpp
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syntax_tree_traversal.cpp
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#include <iostream>
#include <string>
#include <stack>
using namespace std;
struct Node {
string value;
Node* left;
Node* right;
};
Node* newNode(string v) {
Node* temp = new Node;
temp->left = temp->right = NULL;
temp->value = v;
return temp;
}
bool isOperator(char c) {
if (c == '+' || c == '-' || c == '*' || c == '/') {
return true;
}
return false;
}
Node* constructTree(string postfixExpression) {
stack<Node*> st;
Node* t, *t1, *t2;
for (int i = 0; i < postfixExpression.length(); i++) {
if (!isOperator(postfixExpression[i])) {
t = newNode(string(1, postfixExpression[i])); // convert char to string
st.push(t);
}
else {
t = newNode(string(1, postfixExpression[i])); // convert char to string
t1 = st.top();
st.pop();
t2 = st.top();
st.pop();
t->right = t1;
t->left = t2;
st.push(t);
}
}
t = st.top();
st.pop();
return t;
}
int eval(Node* root) {
if (root == NULL)
return 0;
if (!root->left && !root->right)
return stoi(root->value);
int left_sum = eval(root->left);
int right_sum = eval(root->right);
if (root->value == "+")
return left_sum + right_sum;
if (root->value == "-")
return left_sum - right_sum;
if (root->value == "*")
return left_sum * right_sum;
return left_sum / right_sum;
}
int main() {
string postfixExpression;
cout << "Enter the postfix expression: ";
cin >> postfixExpression;
Node* r = constructTree(postfixExpression);
cout << "The result of the expression is: " << eval(r) << endl;
return 0;
}