Problem p00940 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

int N, M, K;
int a[300];
int b[300][300];
int cnt[300];

int s[200000], t[200000];

int A[300];
int B[300][300];
bool check(int x) {
  for (int i = 0; i < M; i++) {
    A[i] = a[i];
  }
  for (int i = 0; i < N; i++) {
    cnt[i] = 0;
    for (int j = 0; j < M; j++) {
      B[i][j] = b[i][j];
      cnt[i] += b[i][j];
    }
  }

  for (int i = 0; i < x; i++) {
    int p = s[i], q = t[i];
    A[q]--;
    if (A[q] < 0)
      return false;

    B[p][q]--;
    cnt[p]--;
    if (cnt[p] == 0) {
      for (int j = 0; j < M; j++)
        A[j] += b[p][j];
    }
  }

  bool update = true;
  while (update) {
    update = false;
    for (int i = 0; i < N; i++) {
      if (cnt[i] == 0)
        continue;
      bool flg = true;
      for (int j = 0; j < M; j++)
        if (A[j] < B[i][j])
          flg = false;
      if (!flg)
        continue;

      cnt[i] = 0;
      for (int j = 0; j < M; j++)
        A[j] += (b[i][j] - B[i][j]);
      update = true;
    }
  }

  for (int i = 0; i < N; i++) {
    if (cnt[i] > 0)
      return false;
    assert(cnt[i] == 0);
  }
  return true;
}

int main() {
  scanf("%d %d %d", &N, &M, &K);
  for (int i = 0; i < M; i++)
    scanf("%d", &a[i]);
  for (int i = 0; i < N; i++)
    for (int j = 0; j < M; j++)
      scanf("%d", &b[i][j]);

  for (int i = 0; i < K; i++) {
    scanf("%d %d", &s[i], &t[i]);
    s[i]--;
    t[i]--;
  }

  int left = 0, right = K, mid;
  while (left < right) {
    mid = (left + right) / 2;
    if (check(mid))
      left = mid + 1;
    else
      right = mid;
  }

  if (check(K + 1))
    left = -1;
  printf("%d\n", left);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

int N, M, K;
int a[300];
int b[300][300];
int cnt[300];

int s[200000], t[200000];

int A[300];
int B[300][300];
bool check(int x) {
  for (int i = 0; i < M; i++) {
    A[i] = a[i];
  }
  for (int i = 0; i < N; i++) {
    cnt[i] = 0;
    for (int j = 0; j < M; j++) {
      B[i][j] = b[i][j];
      cnt[i] += b[i][j];
    }
  }

  for (int i = 0; i < x; i++) {
    int p = s[i], q = t[i];
    A[q]--;
    if (A[q] < 0)
      return false;

    B[p][q]--;
    cnt[p]--;
    if (cnt[p] == 0) {
      for (int j = 0; j < M; j++)
        A[j] += b[p][j];
    }
  }

  bool update = true;
  while (update) {
    update = false;
    for (int i = 0; i < N; i++) {
      if (cnt[i] == 0)
        continue;
      bool flg = true;
      for (int j = 0; j < M; j++)
        if (A[j] < B[i][j])
          flg = false;
      if (!flg)
        continue;

      cnt[i] = 0;
      for (int j = 0; j < M; j++)
        A[j] += (b[i][j] - B[i][j]);
      update = true;
    }
  }

  for (int i = 0; i < N; i++) {
    if (cnt[i] > 0)
      return false;
    assert(cnt[i] == 0);
  }
  return true;
}

int main() {
  scanf("%d %d %d", &N, &M, &K);
  for (int i = 0; i < M; i++)
    scanf("%d", &a[i]);
  for (int i = 0; i < N; i++)
    for (int j = 0; j < M; j++)
      scanf("%d", &b[i][j]);

  for (int i = 0; i < K; i++) {
    scanf("%d %d", &s[i], &t[i]);
    s[i]--;
    t[i]--;
  }

  int left = 0, right = K, mid;
  while (left < right) {
    mid = (left + right) / 2;
    if (check(mid))
      left = mid + 1;
    else
      right = mid;
  }

  if (check(K))
    left = -1;
  printf("%d\n", left);
  return 0;
}