can someone please explain what's wrong with this code? I'm getting this error in console when I try to run the program.

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

int main()
{
    vector<int> nums = {2,1,9,4,4,56,90,3};

    int target = 8;

    unordered_map<int,int> m;

    for(int i=0;i<nums.size();i  ){
        m[nums[i]] = i;
    }

    int req_num;

    for (int i=0; i<nums.size(); i  ){
        req_num = target - nums[i];

        auto search = m.find(req_num);
        int first = search->first;
        int second = search->second;
        if(first == req_num && second != i){
            cout << second << endl;
        }
    }

    return 0;
}

I'm not sure what I'm doing wrong. If someone can point out my error and explain what I did wrong, that'd be of great help!!

I tried running the program multiple times thinking it might be a build error. I'm getting the same result.

It was working fine until I changed map from ordered to unordered.

CodePudding user response：

I bet you are doing two sum question. The reason for segmentation fault is find() may not always find your req_num in the map. By solving this problem, I modified your code and it works properly.

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

int main()
{
    vector<int> nums = {2,1,9,4,4,56,90,3};

    int target = 8;

    unordered_map<int,int> m;

    for(int i=0;i<nums.size();i  ){
        m[nums[i]] = i;
    }

    int req_num;

    for (int i=0; i<nums.size(); i  ){
        req_num = target - nums[i];

        auto search = m.find(req_num);
        if(search == m.end()) continue;
        int first = search->first;
        int second = search->second;
        if(first == req_num && second != i){
            cout << second << endl;
        }
    }

    return 0;
}

I also modified your code to make more sense.

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

int main()
{
    vector<int> nums = {2,1,9,4,4,56,90,3};

    int target = 8;

    unordered_map<int,int> m;

    for(int i=0;i<nums.size();i  ){
        m[nums[i]] = i;
    }

    int req_num;

    for (int i=0; i<nums.size(); i  ){
        req_num = target - nums[i];

        if(m.find(req_num) != m.end()){
            if(m[req_num]!=i){
                cout << m[req_num] << endl;
            }
        };

    }

    return 0;
}