题解 | #剩下的树#

#include<bits/stdc++.h>
#include<vector>

using namespace std;


int main() {
    int l;//马路的长度
    int m;//M组整数
    while (scanf("%d%d", &l, &m) != EOF) {
        int road[l + 1];
        fill(road, road + l + 1, 0);
        for (int i = 0; i < m; i++) {
            int start;
            int end;
            scanf("%d%d", &start, &end);
            for (int j = start; j <= end; j++) {
                road[j] = 1;
            }
        }
        int count = 0;
        for (int i = 0; i < l + 1; i++) {
            if (road[i] == 0)
                count++;
        }
        printf("%d\n", count);
    }

    return 0;
}