算法1

C++ 代码

// 暴力 o(ml) or 区间合并 o(nlogn)
#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;

const int N = 110;
int n, m;
struct Segment{
    int l, r;
    bool operator< (const Segment &t) const
    {
        return l < t.l;
    }
}seg[N];

int main(){
    cin >> n >> m;
    for (int i = 0; i < m; i ++ ){
        cin >> seg[i].l >> seg[i].r;
    }

    sort(seg, seg + m);

    int L = seg[0].l, R = seg[0].r;
    int sum = 0; 
    for (int i = 1; i < m; i ++ ){
        if (seg[i].l <= R){
            R = max(R, seg[i].r);
        }
        else{
            sum += (R - L + 1);
            L = seg[i].l, R = seg[i].r;
        }
    }
    sum += (R - L + 1);
    cout << n + 1 - sum << endl;
    return 0;
}