2020牛客暑期多校训练营（第二场） G Greater and Greater

思路：bitset优化dp，具体怎么做请看这篇博客 https://www.cnblogs.com/EchoZQN/p/13320776.html

#include <bits/stdc++.h>
using namespace std;
const int maxn = 4e4 + 50;
int INF = 1e9;
int n, m;
bitset<maxn> bit1[maxn], bit2, s;
struct node
{
    int x, st;
} a[maxn * 5], b[maxn];
int id[maxn * 5]; 
bool cmp(node p1, node p2){
    return p1.x < p2.x;
}
int main() {
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i++){
        scanf("%d", &a[i].x);
        a[i].st = i;
    }
    for(int i = 1; i <= m; i++){
        scanf("%d", &b[i].x);
        b[i].st = i;
    }
    sort(a + 1, a + n + 1, cmp);
    sort(b + 1, b + m + 1, cmp);
    int p = 1;
    int cnt = 1;
    for(int i = 1; i <= n; i++){
        int fg = 1;
        while(a[i].x >= b[p].x && p <= m){
            if(fg){
                cnt++;
                bit1[cnt] = bit1[cnt - 1];
                fg = 0;
            }
            bit1[cnt].set(b[p].st - 1);
            p++;
        }
        id[a[i].st] = cnt;
    }

    s[m - 1] = 1;
    int ans = 0;
    for(int i = n; i >= 1; i--){
        bit2 = ((bit2 >> 1) | s) & bit1[id[i]];
        if(bit2[0] == 1) ans++;
    }
    printf("%d\n", ans);

    return 0;
}