在C中打印nxn矩阵的所有可能路径

Question

I have a problem in the printing of all possible paths in the nxn matrix.

Here is my code:

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

void printPath(int x, int y, char path[], int n);  

char path[] = "";

int main(void) {
    int n = 2;
    printPath(0, 0, path, n);
    return 0;
}  

void printPath(int x, int y, char path[], int n) {
    char buff[12];
    sprintf(buff, "( %d , %d )", x, y);
    strcat(path, buff);
    if (x == n - 1 && y == n - 1) {
        printf("%s", path);
        printf("\n");
        return;
    }  

    if (x == n - 1)
        printPath(x, y + 1, path, n);
    else
    if (y == n - 1)
        printPath(x + 1, y, path, n);
    else {
        printPath(x + 1, y, path, n);
        printPath(x, y + 1, path, n);
    }
}

I need output as

( 0 , 0 )( 1 , 0 )( 1 , 1 )
( 0 , 0 )( 0 , 1 )( 1 , 1 )   

But am getting this output

( 0 , 0 )( 1 , 0 )( 1 , 1 )
( 0 , 0 )( 1 , 0 )( 1 , 1 )( 0 , 1 )( 1 , 1 )  

Please let me know what might be problem in my code

Answer 1

Maybe the below code would help.

The problem with your code, was you were not removing the element from the string after the recursive call .

Hence the path still contained the previous value.

The last line in the printPath function does exactly the same. Though it might not be the effective way of doing it. But it should work.

#include <stdio.h>
#include<string.h>  
void printPath(int x,int y,char path[],int n);  

char path[500]="";
int main(void) {
int n=2;
printPath(0,0,path,n);
return 0;
}  

void printPath(int x,int y,char path[],int n){
char buff[12];
sprintf(buff,"( %d , %d )",x,y);
strcat(path,buff);
    if(x==n-1 && y==n-1){
        printf("%s",path);
        printf("\n");

    }  

   else if(x==n-1)
     printPath(x,y+1,path,n);
   else if(y==n-1)
    printPath(x+1,y,path,n);
   else{
    printPath(x+1,y,path,n);
    printPath(x,y+1,path,n);
    }

    int len1 = strlen(path);
    int len2 = strlen(buff);

    path[len1 - len2] = '\0';
}

Answer 2

There are multiple problems in your code:

• The global variable path is too small: char path[] = ""; defines it to have a single element. The code invokes undefined behavior. Note that path does not need to be global. Global variables should be avoided if possible.

• You append the current cell coordinates at each recursion step and they remain there for all subsequent paths. You should instead pass the offset for the next element in the output string.

• You do not test for potential buffer overflows, which will happen if n is sufficiently large.

Here is a corrected and simplified version:

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

static void printPath(int x, int y, int n,
                      char path[], size_t size, size_t pos)
{
    pos += snprintf(path + pos, size - pos, "( %d , %d )", x, y);
    if (pos >= size) {
        fprintf(stderr, "path is too small\n");
        exit(1);
    }
    if (x == n - 1 && y == n - 1) {
        printf("%s\n", path);
    } else {
        if (x < n - 1)
            printPath(x + 1, y, n, path, size, pos);
        if (y < n - 1)
            printPath(x, y + 1, n, path, size, pos);
    }
}

int main(void) {
    char path[1024];

    printPath(0, 0, 2, path, sizeof path, 0);
    return 0;
}