Submission #203617

#	Time	Username	Problem	Language	Result	Execution time	Memory
203617		stefdasca	Kangaroo (CEOI16_kangaroo)	C++14	51 / 100	2095 ms	31740 KiB

kangaroo

#include<bits/stdc++.h>
#define mod 1000000007
using namespace std;
int n, a, b;
inline int add(int a, int b)
{
    if(!b)
        return a;
    int x = a+b;
    if(x >= mod)
        x -= mod;
    else
        if(x < 0)
            x += mod;
    return x;
}
int dp[2][2002][2002];
int sp[2][2][2002][2002];
int main()
{
    cin >> n >> a >> b;
    for(int i = 1; i <= n; ++i)
        if(i != a && i != b)
            dp[(a < i)][i - 1 - (a < i)][b - (a < b) - (i < b)] = 1;
    if(n == 2)
    {
        cout << 1;
        return 0;
    }
    int ans = 0;
    for(int sum = n-2; sum >= 1; --sum)
    {
        for(int i = 0; i <= sum; ++i)
            for(int pos = 1; pos <= sum; ++pos)
            {
                int smaller = i;
                int bigger = sum - i;
                if(sum != n-2)
                {
                    dp[0][smaller][pos] = add(sp[0][0][smaller][pos], (smaller > 0) * dp[0][smaller - 1][pos]);
                    dp[1][smaller][pos] = add(sp[0][1][smaller][pos], (smaller > 0) * dp[1][smaller - 1][pos]);
                }
                if(!dp[0][smaller][pos] && !dp[1][smaller][pos])
                    continue;
             //   cout << sum << '\n';
               // cout << smaller << " " << bigger << " " << pos << '\n';
               // cout << dp[0][smaller][bigger][pos] << " " << dp[1][smaller][bigger][pos] << '\n';
                if(sum == 1)
                {
                    if(smaller)
                        ans = add(ans, dp[1][smaller][1]);
                    else
                        ans = add(ans, dp[0][smaller][1]);
                }
                else
                {
                    if(pos <= smaller)
                    {
                        if(pos != 1)
                        {
                            sp[1][0][0][pos - 1] = add(sp[1][0][0][pos - 1], dp[1][smaller][pos]);
                            sp[1][0][pos - 1][pos - 1] = add(sp[1][0][pos - 1][pos - 1], -dp[1][smaller][pos]);
                        }

                        if(pos != smaller)
                        {
                            sp[1][0][pos][pos] = add(sp[1][0][pos][pos], dp[1][smaller][pos]);
                            sp[1][0][smaller][pos] = add(sp[1][0][smaller][pos], -dp[1][smaller][pos]);
                        }

                        if(smaller != sum)
                        {
                            sp[1][1][smaller][pos] = add(sp[1][1][smaller][pos], dp[0][smaller][pos]);
                            sp[1][1][sum][pos] = add(sp[1][1][sum][pos], -dp[0][smaller][pos]);
                        }
                    }
                    else
                    {
                        if(pos != smaller)
                        {
                            sp[1][0][0][pos - 1] = add(sp[1][0][0][pos - 1], dp[1][smaller][pos]);
                            sp[1][0][smaller][pos - 1] = add(sp[1][0][smaller][pos - 1], -dp[1][smaller][pos]);
                        }

                        if(pos - 1 != smaller)
                        {
                            sp[1][1][smaller][pos - 1] = add(sp[1][1][smaller][pos - 1], dp[0][smaller][pos]);
                            sp[1][1][pos - 1][pos - 1] = add(sp[1][1][pos - 1][pos - 1], -dp[0][smaller][pos]);
                        }

                        if(pos != sum)
                        {
                            sp[1][1][pos][pos] = add(sp[1][1][pos][pos], dp[0][smaller][pos]);
                            sp[1][1][sum][pos] = add(sp[1][1][sum][pos], -dp[0][smaller][pos]);
                        }
                    }
                }
            }
        for(int x = 0; x <= 1; ++x)
            for(int q = 0; q <= sum; ++q)
            {
                memcpy(sp[0][x][q], sp[1][x][q], 4 * (sum + 1));
                memset(sp[1][x][q], 0, 4 * (sum + 1));
              //  for(int p = 0; p <= sum; ++p)
                //    sp[0][x][q][p] = sp[1][x][q][p], sp[1][x][q][p] = 0;
            }
    }
    cout << ans;
    return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:37:21: warning: unused variable 'bigger' [-Wunused-variable]
                 int bigger = sum - i;
                     ^~~~~~

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 0 / 49