2020-09-01 校门外的树

https://www.luogu.com.cn/problem/P1047

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <sstream>
#include <algorithm>
#include <cstring>
#include <vector>
using namespace std;

long long qmi(int m, int k)
{
    int res = 1, t = m;
    while (k)
    {
        if (k&1) res = res * t;
        t = t * t;
        k >>= 1;
    }
    return res;
}

int read(){
    int x = 0,f = 1;
    char c = getchar();
    while (c<'0'||c>'9') {
        if (c=='-') {
            f = -1;
        }
        c = getchar();
    }
    while (c>='0'&&c<='9') {
        x = x*10+c-'0';
        c = getchar();
    }
    return x*f;
}

#define fi(a,b) for(int i = a; i <= b; i++)
#define fj(a,b) for(int j = a; j >= b; j--)

//以上不解释
int L,M;
//变量名称与原题相同
int cnt = 0;
//剩余树的数目
int vis[10000 + 10];
//用来判断树木有没有被访问过
int main(){
    L = read();
    M = read();//标准输入，不解释
    for(int i=1 ; i<=M; i++){
        //定义区间的头和尾
        int head = read();
        int tail = read();
        for(int j= head ; j <= tail; j++)
            if(vis[j] == 0)
                vis[j] = 1;//从这个区间的头和尾开始，将所有区间内的树标记为访问过
    }
    for(int i=0; i<= L;i++){
        if(vis[i] == 0)
            cnt++;//计算未被访问过的树的数目
    }
    cout<<cnt<<endl;
    return 0;
}
/*
500 3
150 300
100 200
470 471
============
298
*/