按字母顺序将 2 个字符串组合到另一个字符串中

Question

我想编写一个递归函数，将 2 个字符串组合成一个按字母顺序排列的字符串，这 2 个字符串只是小写字母，并且按字母顺序升序排列。例子 :s1: "aegiz"s2: "abhxy"s3: "aabeghixyz"

总的来说，我对递归函数和 C 仍然是新手，我认为这可以用比我所做的更好的方式解决...

到目前为止我的代码:

#include <stdio.h> 
#include <conio.h>
#include <stdlib.h>
#define N 50
char *combinealph(char *str1, char *str2, char *str3);
void main()
{
	char *str1[N], *str2[N],*str3;
	int length;
	printf("Enter first string:\n");
	gets(str1);
	printf("Enter second string:\n");
	flushall(1);
	gets(str2);
	length = strlen(str1) + strlen(str2);
	str3 = (char*)malloc((length+1)*sizeof(char));
	printf("The combined string :\n");
	puts(combinealph(str1, str2, str3));
	getch();
}

char *combinealph(char *str1, char *str2, char *str3)
{
	if (*str1 == '\0' && *str2 != '\0')
		strcpy(str3, str2);
		return str3;
	if (*str1 != '\0' && *str2 == '\0')
		strcpy(str3, str1);
		return str3;
	if (*str1 == '\0' && *str2 == '\0')
			return '\0';

	if (*str1 >= *str2)
	{
		strcpy(str3, str1);
		return strcat(*str3, combinealph(str1 + 1, str2, str3+1));
	}
	if (*str1 < *str2)
	{
		*str3 = *str2;	
		return strcat(*str3, combinealph(str1, str2 + 1, str3+1));
	}
}

Answer 1

看来你的意思是下面的

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

char * combine_strings( char *result, const char *s1, const char *s2 )
{
    if ( *s1 == '\0' && *s2 == '\0' )
    {
        *result = '\0';
        return result;
    }
    else if ( *s1 == '\0' )
    {
        *result++ = *s2++;
        return combine_strings( result, s1, s2 ) - 1;
    }
    else if ( *s2 == '\0' )
    {
        *result++ = *s1++;
        return combine_strings( result, s1, s2 ) - 1;
    }
    else
    {
        *result++ = *s2 < *s1 ? *s2++ : *s1++;
        return combine_strings( result, s1, s2 ) - 1;
    }        
}    

int main(void)
{
    const char *s1 = "aegiz"; 
    const char *s2 = "abhxy";
    char result[ strlen( s1 ) + strlen( s2 ) + 1];

    printf( "%s\n", combine_strings( result, s1, s2 ) );

    return 0;
}

程序输出为

aabeghixyz

您可以缩短函数。例如

char * combine_strings( char *result, const char *s1, const char *s2 )
{
    if ( *s1 == '\0' && *s2 == '\0' )
    {
        *result = '\0';
        return result;
    }
    else
    {
        *result++ = ( *s2 && *s2 < *s1 ) || !*s1 ? *s2++ : *s1++;
        return combine_strings( result, s1, s2 ) - 1;
    }        
}