Zbrka

#include <bits/stdc++.h>
#define P 1000000007
#define ll long long

using namespace std;

ll d[2][1010101], z = 1, s = 0;

int main(){
    int n, c;
    cin >> n >> c;

    d[1][1] = 1;

    for(int i=1; i<=n; i++){
        z += i-1;
        int h = (z+1)/2;
        for(int j=1; j<=h && j<=c+1; j++){
            d[s][j] = d[s][j-1]+d[s^1][j];
            if(j>i) d[s][j] -= d[s^1][j-i];
            if(d[s][j]<0) d[s][j]+=P;
            d[s][j]%=P;
        }

        if(z&1){
            for(int j=1; j<h && j<=c+1; j++){
                d[s][j+h] = d[s][h-j];
            }
        } else {
            for(int j=1; j<h+1 && j<=c+1; j++){
                d[s][j+h] = d[s][h-j+1];
            }
        }

        s^=1;
    }

    cout << d[s^1][c+1];
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED