This answer is a bit different, it assumes you are loading a tree of integer values from a string, that could be loaded from a file. Next time you ask a question about code, could you please explain a little bit what the code does? Guessing does take some time and some effort.
I've reused the main() and PrintTree() functions from Khurshid Normuradov's answer. I hope he won't mind.
I took the liberty to add modern c++ coding techniques because this question is tagged c++17, so you're getting an example in c++17.
#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <string_view>
struct Node {
std::unique_ptr<Node> left = nullptr;
std::unique_ptr<Node> right = nullptr;
int value = 0;
};
std::unique_ptr<Node> treeFromString(std::string_view str) {
std::cout << "treeFromString(\"" << str << "\")\n";
if (str.empty()) return {};
auto node = std::make_unique<Node>();
// extract an int
auto pos = str.find_first_not_of("0123456789");
auto val = str.substr(0, pos);
// optional: std::stoi() would throw anyway in this case
if (val.empty())
throw std::runtime_error("invalid value in expression");
node->value = std::stoi(std::string{val});
if (val.length() == str.length()) return node;
str = str.substr(val.length());
// Both left/right parsing are similar and use this
// common subroutine.
// expects parens delimited string as input.
// param str in: str string to parse from
// out: whatever's left to parse
// returns string content within parens, parens not included.
auto extract_parens_contents = [](std::string_view& str) {
// right here would be the perfect place to insert code to skip
// whitespace if you ever needed to do that.
// find parens extent
int parens = 0;
auto parens_end =
std::find_if(str.begin(), str.end(), [&parens](char c) {
parens += (c == '(') - (c == ')');
return (parens == 0);
});
if (parens_end == str.end())
throw std::runtime_error("unbalanced parens in expression");
// extract result
auto result = std::string_view(
str.begin() + 1, std::distance(str.begin() + 1, parens_end));
// remove spent bytes from input stream
str = std::string_view(
parens_end + 1,
str.length() - std::distance(str.begin(), parens_end + 1));
return result;
};
node->left = treeFromString(extract_parens_contents(str));
node->right = treeFromString(extract_parens_contents(str));
return node;
}
// special thanks to user Khurshid Normuradov, who originally wrote the two functions below.
// it would be difficult to writing something that would be any better for the
// intended purpose.
void printTree(Node* root, int level = 0) {
if (root == nullptr) return;
for (int i = 0; i < level; ++i) std::cout << "--";
std::cout << " data = " << root->value << std::endl;
printTree(root->left.get(), level + 1);
printTree(root->right.get(), level + 1);
}
int main() {
std::string str = "12(8(7)(5))(9(3)(2(1)(8)))";
auto expr = treeFromString(str);
printTree(expr.get());
}
You can play with the code here: https://godbolt.org/z/ch3zv5KTT
