校门外的树（前缀数组）

#include<iostream>#include<algorithm>#include<stdio.h>#include<string.h>using namespace std;#define fr(i,a,b) for(int i=(a),i_end=(b);i<=i_end;i++)#define frd(i,a,b) for(int i=(a),i_end=(b);i>=i_end;i--)#define ll long long#define pri(x) printf("%d",x)#define mes(x) memset(x,0,sizeof(x))#define prin(x) printf("%d\n",x)#define ln putchar('\n')using namespace std;int l,n,x,y,d,s,f[10000100];int main(){    scanf("%d%d",&l,&n);    for(int i=1;i<=n;i++){        scanf("%d%d",&x,&y);        f[x]++;        f[y+1]--;    }    d=0;    s=0;    for(int i=0;i<=l;i++){        d+=f[i];        s+=(d==0);    }    printf("%d",s);    return 0;}