Problem p02277 (C++) — buggy submission, verdict: Runtime Error

#include <stdio.h>

#define MAX 100000
#define SENTINEL 2000000000

struct Card {
  char suit;
  int value;
};

struct Card L[MAX / 2 + 2], R[MAX / 2 + 2];

void merge(struct Card A[], int n, int left, int mid, int right) {
  int i, j, k;
  int n1 = mid - left;
  int n2 = right - mid;
  for (i = 0; i < n1; i++)
    L[i] = A[left + i];
  for (i = 0; i < n2; i++)
    R[i] = A[mid + i];
  L[n1].value = R[n2].value = SENTINEL;
  i = j = 0;
  for (k = left; k < right; k++) {
    if (L[i].value <= R[j].value) {
      A[k] = L[i++];
    } else {
      A[k] = R[j++];
    }
  }
}

void mergeSort(struct Card A[], int n, int left, int right) {
  int mid;
  if (left + 1 < right) {
    mid = (left + right) / 2;
    mergeSort(A, n, left, mid);
    mergeSort(A, n, mid, right);
    merge(A, n, left, mid, right);
  }
}

int partition(struct Card A[], int n, int p, int r) {
  int i, j;
  struct Card t, x;
  x = A[r];
  i = p - 1;
  for (j = p; j < r; j++) {
    if (A[j].value <= x.value) {
      i++;
      t = A[i];
      A[i] = A[j];
      A[j] = t;
    }
  }
  t = A[i + 1];
  A[i + 1] = A[r];
  A[r] = t;
  return i + 1;
}

void quickSort(struct Card A[], int n, int p, int r) {
  int q;
  if (p < r) {
    q = partition(A, n, p, r);
    quickSort(A, n, p, q - 1);
    quickSort(A, n, q + 1, r);
  }
}

int main() {

  int n, i, v;
  struct Card A[MAX], B[MAX];
  char S[10];
  int stable = 1;

  scanf("%d", &n);

  for (i = 0; i < n; i++) {
    scanf("%s %d", S, &v);
    A[i].suit = B[i].suit = S[0];
    A[i].value = B[i].value = v;
  }

  mergeSort(A, n, 0, n);
  quickSort(B, n, 0, n - 1);

  for (i = 0; i < n; i++) {
    if (A[i].suit != B[i].suit) {
      stable = 0;
      break;
    }
  }

  if (stable == 1)
    printf("Stable\\n");
  else
    printf("Not stable\\n");
  for (i = 0; i < n; i++) {
    printf("%c %d\\n", B[i].suit, B[i].value);
  }

  return 0;
}

Error: WA

Fixed submission:

#include <stdio.h>

#define MAX 100000
#define SENTINEL 2000000000

struct Card {
  char suit;
  int value;
};

struct Card L[MAX / 2 + 2], R[MAX / 2 + 2];

void merge(struct Card A[], int n, int left, int mid, int right) {
  int i, j, k;
  int n1 = mid - left;
  int n2 = right - mid;
  for (i = 0; i < n1; i++)
    L[i] = A[left + i];
  for (i = 0; i < n2; i++)
    R[i] = A[mid + i];
  L[n1].value = R[n2].value = SENTINEL;
  i = j = 0;
  for (k = left; k < right; k++) {
    if (L[i].value <= R[j].value) {
      A[k] = L[i++];
    } else {
      A[k] = R[j++];
    }
  }
}

void mergeSort(struct Card A[], int n, int left, int right) {
  int mid;
  if (left + 1 < right) {
    mid = (left + right) / 2;
    mergeSort(A, n, left, mid);
    mergeSort(A, n, mid, right);
    merge(A, n, left, mid, right);
  }
}

int partition(struct Card A[], int n, int p, int r) {
  int i, j;
  struct Card t, x;
  x = A[r];
  i = p - 1;
  for (j = p; j < r; j++) {
    if (A[j].value <= x.value) {
      i++;
      t = A[i];
      A[i] = A[j];
      A[j] = t;
    }
  }
  t = A[i + 1];
  A[i + 1] = A[r];
  A[r] = t;
  return i + 1;
}

void quickSort(struct Card A[], int n, int p, int r) {
  int q;
  if (q < r) {
    q = partition(A, n, p, r);
    quickSort(A, n, p, q - 1);
    quickSort(A, n, q + 1, r);
  }
}

int main() {

  int n, i, v;
  struct Card A[MAX], B[MAX];
  char S[10];
  int stable = 1;

  scanf("%d", &n);

  for (i = 0; i < n; i++) {
    scanf("%s %d", S, &v);
    A[i].suit = B[i].suit = S[0];
    A[i].value = B[i].value = v;
  }

  mergeSort(A, n, 0, n);
  quickSort(B, n, 0, n - 1);

  for (i = 0; i < n; i++) {
    if (A[i].suit != B[i].suit) {
      stable = 0;
      break;
    }
  }

  if (stable == 1)
    printf("Stable\\n");
  else
    printf("Not Stable\\n");
  for (i = 0; i < n; i++) {
    printf("%c %d\\n", B[i].suit, B[i].value);
  }

  return 0;
}