题解 | 茉茉的密码

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>

int main(void) {
    int n;
    if (scanf("%d", &n) != 1) {
        return 1;
    }
    int c;
    while ((c = getchar()) != '\n' && c != EOF);

    bool is_common[26];
    for (int i = 0; i < 26; i++) {
        is_common[i] = true;
    }
    for (int i = 0; i < n; i++) {
        char* s = malloc(100000 * sizeof(char));
        if (s == NULL) {
            return 1;
        }
        if (fgets(s, 100000, stdin) == NULL) {
            free(s);
            return 1;
        }
        s[strcspn(s, "\n")] = 0;

        bool current_exists[26] = {false};
        int len = strlen(s);

        for (int j = 0; j < len; j++) {
            char c = s[j];
            if (c >= 'a' && c <= 'z') {
                current_exists[c - 'a'] = true;
            }
        }
        for (int j = 0; j < 26; j++) {
            if (!current_exists[j]) {
                is_common[j] = false;
            }
        }
        free(s);
    }
    for (int i = 0; i < 26; i++) {
        if (is_common[i]) {
            printf("%c\n", 'a' + i);
            return 0;
        }
    }
    return 0;
}