HJ58 Input n integers, output the smallest k among them

The topic is not difficult, and the basic knowledge of arrays is examined. Therefore, I fell into the pit, and the basic knowledge is not solid.

Various problems arose with my various solutions:

1 Multiple groups of input problems

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main()
{
    int n;
    int m;
    int r;
    int i=0;
    vector<int>v;
    cin>>n>>m;
    while(n--)
    {
        cin>>r;
        v.push_back(r);
    }
    sort(v.begin(),v.end());
    while(m--)
    {
        
        cout<<v[i]<<" ";
        i++;
    }
    return 0;
}

Because I am not used to this cin double input problem, it is always easy to write it as a single input problem;

2 Local variables and global variables

int main()
{
    int n;
    int m;
    int r;
    int i=0;
    vector<int>v;
    while(cin>>n>>m)
    {
        for(int i=0;i<n;i++)
        {
            cin>>r;
            v.push_back(r);
        }
        sort(v.begin(),v.end());
        while(m--)
        {
            cout<<v[i]<<" ";
            i++;
        }
    }
    return 0;
}

This problem also occurs in 1. When printing, the i in the output v[i] should be set as a local variable, otherwise multiple sets of input will be wrong.

3 Array insertion problem

int main()
{
    int n;
    int m;
    
    while (cin >> n >> m)
    {
        vector<int>v;
        for (int i = 0; i < n; i++)
        {
           cin>>v.at(i);//cin>>v[i];
        }
        sort(v.begin(), v.end());
        int j=0;
        while(m--)
        {
          cout <<v[j]<<" ";
           j++;
         
        }
        cout << endl;
    }
    return 0;
}

The answer prompts access to out-of-bounds overflow and other issues. After debugging, the problem appears that v is not given a certain space size when it is defined, so an error is reported.

Change it to:

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main()
{
    int n;
    int m;
    
    while (cin >> n >> m)
    {
        vector<int>v(n);
        for (int i = 0; i < n; i++)
        {
           cin>>v.at(i);
        }
        sort(v.begin(), v.end());
        int j=0;
        while(m--)
        {
          cout <<v[j]<<" ";
           j++;
         
        }
        cout << endl;
    }
    return 0;
}

Summarize:

1. Pay attention to the problem of global variables;

2. You can use v.push_back() for container insertion. When using v[i]/v.at(i), you need to define the size of the array to prevent out of bounds!

In short, pay attention to the details! ! ! !