Inserted in set and received Segmentation fault - c++

Question

I created code to convert graph representation (A list of edges -> the adjacency list)
How can i fix error?
I have Segmentation fault in line res[cur.first - 1].insert(cur.second);for input
4 3
3 2
2 1
4 2
My code
#include <bits/stdc++.h>
using namespace std;
pair<int, int> strToSotredPair(const string& s) {
int a = 0, b = 0;
int pos = 0;
while (s[pos] != ' ') {
a = a * 10 + s[pos] - '0';
++pos;
}
while (pos < s.size()) {
b = b * 10 + s[pos] - '0';
++pos;
}
return {min(a, b), max(a, b)};
}
int main() {
int n, m;
string input;
cin >> n;
cin >> m;
vector<set<int>> res(n, set<int>());
for (int i = 0; i < m; ++i) {
cin >> input;
auto cur = strToSotredPair(input);
res[cur.first - 1].insert(cur.second); // error in this line
}
for (int i = 0; i < res.size(); ++i) {
cout << res[i].size() << ' ';
for (auto item : res[i]) {
cout << item << ' ';
}
cout << endl;
}
}

Answer 1

There are a couple of error's in your code because of which you were getting that error.
You wanted the graph edges as strings. So you need to take edge inputs as strings. For that, you would be required to use getline(cin,input) and cin.ignore().
(My suggestion: Do not take inputs as strings because as it is you are converting them to integers afterwards. By default if you just write cin<<node1<<node2; the two nodes of an edge would have come as integers and function strToSotredPair would not be needed).
In function strToSotredPair after you get the integer a, pos variable is pointing to the space. So you need to increase it by 1 to point to the starting position to 2nd number. Hence a pos++ was needed.
#include <bits/stdc++.h>
using namespace std;
pair<int, int> strToSotredPair(const string& s) {
int a = 0, b = 0;
int pos = 0;
while (s[pos] != ' ') {
a = a * 10 + s[pos] - '0';
++pos;
}
pos++;
while (pos < s.size()) {
b = b * 10 + s[pos] - '0';
++pos;
}
return {min(a, b), max(a, b)};
}
int main() {
int n, m;
string input;
cin >> n;
cin >> m;
vector<set<int>> res(n, set<int>());
cin.ignore(); // To clear the input buffer
for (int i = 0; i < m; ++i) {
getline(cin, input); // to get line by line string inputs
auto cur = strToSotredPair(input);
res[cur.first - 1].insert(cur.second);
}
for (int i = 0; i < res.size(); ++i) {
cout << res[i].size() << ' ';
for (auto item : res[i]) {
cout << item << ' ';
}
cout << endl;
}
}