Submission #1078984

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Source Code Expand

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#endif

#include <bits/stdc++.h>

using namespace std;

mt19937 mrand(random_device{} ()); 

int rnd(int x) {
  return mrand() % x;
}

typedef long double ld;
typedef long long ll;

#ifdef DEBUG
#define eprintf(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#else
#define eprintf(...) ;
#endif

#define pb push_back
#define mp make_pair
#define sz(x) ((int) (x).size())
#define TASK "text"

const int inf = (int) 1.01e9;
const ld eps = 1e-9;
const ld pi = acos((ld) -1.0);

const int mod = (int) 1e9 + 7;

void add(int &x, int y) {
  if ((x += y) >= mod) {
    x -= mod;
  }
}

int mult(int x, int y) {
  return (long long) x * y % mod;
}

int myPower(int x, int pw) {
  int res = 1;
  for (; pw; pw >>= 1) {
    if (pw & 1) {
      res = mult(res, x);
    }
    x = mult(x, x);
  }
  return res;
}

void precalc() {
}


const int maxn = (int) 2e3 + 10;
int n, m, k;

int read() {
  if (scanf("%d%d%d", &n, &m, &k) < 3) {
    return 0;
  }
  return 1;
}

const int maxc = maxn * 3;
int dp[maxc][maxc];

void solve() {
  memset(dp, 0, sizeof(dp));
  for (int r = 1; r < k; ++r) {
    add(dp[r][k - r], 1);
    add(dp[r + 1][k - r - 1], mod - 1);
  }
  int res = 0;

  const int M = n + m;
  for (int x = 0; x <= M; ++x) {
    for (int y = 0; y <= M; ++y) {
      int cur = dp[x][y];
      if (!cur) {
        continue;
      }
      //eprintf("dp[%d][%d] = %d\n", x, y, cur);
      if (y) {
        add(dp[x + 1][y - 1], cur);
      }

      if (x <= n && y <= m && (n - x) % (k - 1) == 0 && (m - y) % (k - 1) == 0) {
        add(res, cur);
      }
      add(dp[x][y + k - 1], cur);
      if (y) {
        add(dp[x + k][y - 1], mod - cur);
      }
    }
  }
  printf("%d\n", res);
}

int main() {
  precalc();
#ifdef LOCAL
  freopen(TASK ".out", "w", stdout);
  assert(freopen(TASK ".in", "r", stdin));
#endif

  while (1) {
    if (!read()) {
      break;
    }
    solve();
#ifdef DEBUG
    eprintf("Time %.2f\n", (double) clock() / CLOCKS_PER_SEC);
#endif
  }
  return 0;
}

Submission Info

Judge Result