题解 | 校门外的树

#include <limits.h>
#include <stdio.h>

int main() {
    int L, M;
    scanf("%d %d", &L, &M);

    //总共有L + 1棵树
    //M代表区域的个数

    int sum = 0;
    int shuzu[L + 1];
    for (int i = 0; i < L + 1; i++){
        shuzu[i] = 0;
    }
    while (M--) {
        int a, b;
        scanf("%d %d", &a, &b);
        //闭区间输入

        if (b > L || b < 0 || a > L || a < 0){
            return 0;
        }
        if (a > b){
            int c = b;
            b = a;
            a = c;
        }

        for (int i = a; i <= b; i++){
            shuzu[i] = 1;
        }
    }
    
    int count = 0;
    for (int i = 0; i < L + 1; i++){
        if (shuzu[i] == 0){
            count++;
        }
    }
    printf("%d", count);    
    return 0;
}