题解 | 校门外的树

#include <iostream>
#include <vector>

using namespace std;//这个写法在小项目可以用，在大项目里有潜在问题

int main() 
{
    int L = 0;
    int M = 0;
    int i = 0;
    int r = 0;
    int sum = 0;
    cin>>L>>M;

    vector <bool> tree(L + 1,true);

    for (int i1 = 1;i1 <= M;i1++)
    {
        cin>>i>>r;
        for (int i2 = i;i2 <= r;i2++)
        {
            tree[i2] = false;
        }
    }

    for (int i3 = 0;i3 <= L;i3++)
    {
        if (tree[i3])
        {
            sum++;
        }
    }

    cout<<sum;
}