题解 | 剩下的树

#include <iostream>
#include <stack>
#include <string>
#include<queue>
#include<vector>
#include<list>//双向链表
using namespace std;
int main() {
	int l; int m;
	while (cin >> l>>m) {
		vector<int> l1(l+1);
		vector<int>::iterator it;
		for (it = l1.begin(); it != l1.end(); it++) {
			*it = 1;
		}
		for (int i = 0; i < m; i++) {
			int a, b;
			cin >> a >> b;
			for (int i = a; i < b + 1; i++) {
				l1[i] = 0;
			}
		}
		int sum = 0;
		for (it = l1.begin(); it != l1.end(); it++) {
			sum += *it;
		}
		cout << sum << endl;
	}
}