merge

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define M 20 // 数组元素最多个数
#define N 15 // 单词最大长度，包括 '\0'

size_t gets_to_array(char a[][N]) {
    int ch, last_space = 0;
    size_t i = 0, j = 0;
    while (ch = getchar(), ch != EOF && ch != '\n') {
        if (isspace(ch)) {
            if (!last_space) {
                a[i++][j] = '\0';
                last_space = 1;
                j = 0;
            }
        } else {
            a[i][j++] = (char)ch;
            last_space = 0;
        }
    }
    return i + 1;
}

int cmp_str(const void *a, const void *b) {
    return strcmp(a, b);
}

size_t merge_arrays(char a[][N], size_t n, char b[][N], size_t m, char c[][N]) {
    qsort(a, n, sizeof(a[0]), cmp_str);
    qsort(b, m, sizeof(b[0]), cmp_str);
    size_t i, j, k;
    for (i = 0, j = 0, k = 0; i < n && j < m;) {
        if (strcmp(a[i], b[j]) <= 0) {
            if (k == 0 || strcmp(c[k - 1], a[i]) != 0)
                strcpy(c[k++], a[i]);
            i++;
        } else {
            if (k == 0 || strcmp(c[k - 1], b[j]) != 0)
                strcpy(c[k++], b[j]);
            j++;
        }
    }
    for (; i < n; ++i)
        if (k == 0 || strcmp(c[k - 1], a[i]) != 0)
            strcpy(c[k++], a[i]);
    for (; j < m; ++j)
        if (k == 0 || strcmp(c[k - 1], b[j]) != 0)
            strcpy(c[k++], b[j]);
    return k;
}

void show_array(char a[][N], size_t n) {
    printf("{ ");
    for (size_t i = 0; i < n; ++i) {
        printf(i == n - 1 ? "%s" : "%s, ", a[i]);
    }
    printf(" }\n");
}

int main() {
    char A[M][N];
    char B[M][N];
    char C[M * 2][N];

    size_t lenA = gets_to_array(A);
    size_t lenB = gets_to_array(B);
    size_t lenC = merge_arrays(A, lenA, B, lenB, C);

    show_array(A, lenA);
    show_array(B, lenB);
    show_array(C, lenC);
}