[Review] NOIP exam topics Luogu P1047

Thinking

Similarly prefix and safeguard what the difference is like.

Code

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
int a[10005],n,m,ans=0;
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        a[x]++,a[y+1]--;
    }
    ans=(a[0]==0);
    for (int i=1;i<=n;i++)
    {
        a[i]+=a[i-1];
        if (a[i]==0) ans++;
    }
    cout<<ans;
    return 0;
}