Luogu3740 [HAOI2014]贴海报 （线段树）

倒着来

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("\n\n----------\n\n")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

const int N = 1007;

struct Post{
    int l, r;
}a[N];

int flag;
int t[40000003];
#define lson rt << 1, l, mid
#define rson rt << 1 | 1, mid + 1, r
inline void Pushup(int rt){
    t[rt] = t[rt << 1] && t[rt << 1 | 1];
}
inline void Updata(int rt, int l, int r, int L, int R){
    if(t[rt]) return;
    if(L <= l && r <= R){
        t[rt] = 1;
        flag = 1;
        return;
    }
    int mid = (l + r) >> 1;
    if(L <= mid)
        Updata(lson, L, R);
    if(R > mid)
        Updata(rson, L, R);
    Pushup(rt);
}

int main(){
    int LEN ,n;
    io >> LEN >> n;
    R(i,1,n){
        io >> a[i].l >> a[i].r;
    }

    int ans = 0;
    nR(i,n,1){
        flag = 0;
        Updata(1, 1, LEN, a[i].l, a[i].r);
        ans += flag;
    }
    
    printf("%d", ans);
    
    return 0;
}