bool标记

#include <iostream>
#include <cstring>
using namespace std;

int main(){
int l, m;
cin >> l >> m;
bool tree[10001];
memset(tree, 0, sizeof(tree));

for (int i =0; i < m; i++){
    int u, v;
    cin >> u >> v;
    for(int j = u; j <= v; j++){
        tree[j] = true;
        
    }
}

int removed = 0;
for(int j = 0; j <= l; j++){
    if(tree[j]){
        removed++;
    }
}

cout << l + 1 - removed << endl;
return 0;

}