Syntax error for the code found in a tutorial? - c++

Question

I was learning to do a program online and found this solution and I wanted to execute and learn from it.
I am keep getting syntax error, can someone help with formatting it? I tried but couldn't understand the code that much to see where we need to provide indentation etc.,
I couldn't find a python example online for that question, I could only find c++ answer.
class Node {
public:
virtual int Compute() = 0;
inline void SetLeft(Node* left) {
left_ = left;
}
inline void SetRight(Node* right) {
right_ = right;
}
protected:
Node* left_ = nullptr;
Node* right_ = nullptr;
};
class SumNode : public Node {
public:
inline int Compute() override {
return left_->Compute() + right_->Compute();
}
};
class SubNode : public Node {
public:
inline int Compute() override {
return left_->Compute() - right_->Compute();
}
};
class MulNode : public Node {
public:
inline int Compute() override {
return left_->Compute() * right_->Compute();
}
};
class NumNode : public Node {
public:
NumNode(int num) : num_(num) {}
inline int Compute() override {
return num_;
}
private:
int num_;
};
class Solution {
public:
vector<int> diffWaysToCompute(string expression) {
vector<Node*> nodes;
// parse the expression
for(int i = 0; i < expression.size(); ++i) {
switch(expression[i]) {
case '+':
nodes.emplace_back(new SumNode());
break;
case '-':
nodes.emplace_back(new SubNode());
break;
case '*':
nodes.emplace_back(new MulNode());
break;
default:
int num = 0;
while(expression[i] >= '0' && expression[i] <= '9') {
num = num * 10 + expression[i] - '0';
++i;
}
--i;
nodes.emplace_back(new NumNode(num));
break;
}
}
vector<Node*> trees = GenerateAllTrees(nodes, 0, nodes.size() - 1);
for(Node* node : nodes) {
delete node;
}
vector<int> results;
for(Node* tree : trees) {
results.emplace_back(tree->Compute());
delete tree;
}
return results;
}
vector<Node*> GenerateAllTrees(const vector<Node*> nodes, int beg, int end) {
if(beg == end) {
return {new NumNode(nodes[beg]->Compute())};
}
vector<Node*> results;
for(int i = beg; i <= end; i++) {
// assuming the expression is well formed, operators will be in odd positions
if((i & 1) == 0) continue;
vector<Node*> left_trees = GenerateAllTrees(nodes, beg, i - 1);
vector<Node*> right_trees = GenerateAllTrees(nodes, i + 1, end);
for(Node* left : left_trees) {
for(Node* right : right_trees) {
nodes[i]->SetLeft(left);
nodes[i]->SetRight(right);
Node* result = new NumNode(nodes[i]->Compute());
results.emplace_back(result);
}
}
for(Node* t : left_trees) {
delete t;
}
for(Node* t : right_trees) {
delete t;
}
}
return results;
}
};

Answer 1

You just need to import the modules you are using, exactly like Python, except the syntax is different:
#include <vector>
#include <string>
using namespace std;
class Node {
public:
...
And because it is using emplace_back, if you are using g++, you'll need to specify -std=c++11 on the command line.
Also, you need to understand this is not a runnable example. These are just classes you could use in your own code. To run this, you'll need to supply a main() function. Maybe:
#include <iostream>
int main()
{
Solution s;
vector<int> result = s.diffWaysToCompute( "3+9*7-16" );
for( auto i : result )
cout << i << "\n";
}