牛客小白月赛98补题

D一道很典型的区间DP

//区间DP典题
#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 520;
ll n, L, R;
string s;
ll sum0[N], sum1[N];
ll f[N][N];
void solve()
{
    cin >> n >> L >> R >> s;
    s = ' ' + s;
    for (int i = 1; i <= n; i++)
    {
        sum0[i] = sum0[i - 1] + (s[i] == '0');
        sum1[i] = sum1[i - 1] + (s[i] == '1');
    }

    for (int len = 1; len <= n; len++)//枚举长度
    {
        for (int l = 1; l + len - 1 <= n; l++)//枚举左端点
        {
            if (len == 1)continue;
            int r = l + len - 1;
            for (int k = l; k < r; k++)
            {
                int x = abs(sum0[k] - sum0[l - 1] - sum1[r] + sum1[k]);
                if (L <= x && x <= R)f[l][r] = max(f[l][r], f[l][k] + f[k+1][r] + 1);
            }

        }
    }
    cout << f[1][n] << endl;
}
int main() 
{
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    int t=1;
    //cin >> t;
    while (t--) 
    {
        solve();
    }

    return 0;
}