後輩の課題

sort_alpha.c

#include <ctype.h>
#include <stdio.h>

#define BUF_SIZE  1024
#define N_ALPHA   26
#define LALPHA_TO_NR(c)  (c - 'a')
#define NR_TO_LALPHA(n)  (n + 'a')
#define LENGTH(array)  (sizeof(array) / sizeof((array)[0]))
#define SWAP(type, a, b) \
  do { \
    type __tmp_swap_var__ = *(a); \
    *(a) = *(b); \
    *(b) = __tmp_swap_var__; \
  } while (0)

typedef struct {
  char ch;
  int  cnt;
} Pair;

void init_pairs(Pair *restrict pairs, int n);
void bsort(Pair *restrict pairs, int n);
void show(const Pair *restrict pairs, int n);


int main(void) {
  static char str[BUF_SIZE];
  static Pair pairs[N_ALPHA];
  fgets(str, sizeof(str), stdin);

  init_pairs(pairs, LENGTH(pairs));
  for (const char *restrict ptr = str; *ptr != '\0'; ptr++) {
    if (isalpha(*ptr)) {
      pairs[LALPHA_TO_NR(tolower(*ptr))].cnt++;
    }
  }
  bsort(pairs, LENGTH(pairs));
  show(pairs, LENGTH(pairs));
  return 0;
}


void init_pairs(Pair *restrict pairs, int n) {
  for (int i = 0; i < n; i++) {
    pairs[i].ch = NR_TO_LALPHA(i);
  }
}


void bsort(Pair *restrict pairs, int n) {
  for (int i = 0; i < n - 1; i++) {
    for (int j = n - 1; j > i; j--) {
      if (pairs[j - 1].cnt < pairs[j].cnt) {
        SWAP(Pair, &pairs[j - 1], &pairs[j]);
      }
    }
  }
}


void show(const Pair *restrict pairs, int n) {
  for (int i = 0; i < N_ALPHA; i++) {
    printf("%c(%c): %d\n", pairs[i].ch, toupper(pairs[i].ch), pairs[i].cnt);
  }
}