How to do recursion on multidimensional array

Question

I am new to recursion, I am having trouble getting the right solution on how to do recursion on 2D array. Can you please give me idea how to fix my logic on my code. I think my algorithm is not correct.

I tried to create recursion on some point but its not working.

#include <stdio.h>

#define HEIGHT 21
#define WIDTH 5
int getLowestVertex(int graph[HEIGHT][WIDTH], int currLabel,int height, int width, int labelCount){
    int counter = 0;
    int low_label = 999;
    int j;
    int i;
    int *visitedLabelCheck = NULL;         //This will identify the visted label already
    visitedLabelCheck = (int *)malloc(labelCount * sizeof(int));

    //set all value to 0
    for(i = 0; i < labelCount; i++){
        visitedLabelCheck[i] = 0;
    }
    printf("\n");
    low_label = lowest_label(graph, currLabel, visitedLabelCheck, low_label);

    return low_label;
}

int lowest_label(int link[HEIGHT][WIDTH], int currentLabel, int *visitedLabelCheck, int low_label){
    int currentCounter = 0;
    int lowestLabel = 0;


    while(1) {//loop for the current label vertices  
        if(link[currentLabel][currentCounter] != 0){

            if(visitedLabelCheck[currentLabel] == -1)
                return link[currentLabel][currentCounter];

            if (link[currentLabel][currentCounter] < low_label) {
                low_label = link[currentLabel][currentCounter];
            }
            lowestLabel = lowest_label(link, link[currentLabel][currentCounter], visitedLabelCheck, lowestLabel);
            visitedLabelCheck[currentLabel] = -1;
            if (lowestLabel < low_label){
                return link[currentLabel][currentCounter];
            }
            currentCounter++;
        }else{
            break;
        }
    }
}


int main(int argc, char *argv[]) {

    int testThisVertex;
    int lowestVertex;
    int labelCount;
    int height;
    int width;
    int g[HEIGHT][WIDTH] =   {{1, 21, 0, 0, 0}, //undirected graph
                              {2,  0, 0, 0, 0},
                              {3,  0, 0, 0, 0}, 
                              {4,  5, 0, 0, 0},
                              {5,  4, 0, 0, 0},
                              {6, 21, 0, 0, 0},
                              {7,  8,2, 14, 0},
                              {8,  7, 9, 0, 0},
                              {9,  8,10, 0, 0},
                              {10, 9,11, 0, 0},
                              {11,10, 0, 0, 0},
                              {12,13, 0, 0, 0},
                              {13,12,14, 0, 0},
                              {14,13,15, 7, 0},
                              {15,14, 0, 0, 0},
                              {16, 0, 0, 0, 0},
                              {17, 0, 0, 0, 0},
                              {18, 0, 0, 0, 0},
                              {19,20, 0, 0, 0},
                              {20,19, 0, 0, 0},
                              {21,17,18, 6, 1}};

    //find the least label if input is 12 
    //12 -> 13 
    //      |  \
    //      12  14
    //          | \   \
    //         13  15  7
    //              |   | \  \
    //             14   8  2  14
    //ANSWER: 2
    testThisVertex=12;
    labelCount = 21;
    height = 21;
    width = 5;
    lowestVertex = getLowestVertex(g, testThisVertex, height, width, labelCount);
    printf("\nThe lowest value that is connected to %d vertex is %d", testThisVertex, lowestVertex);

    getchar();
}

The expected output should be the lowest vertex that is connected to the vertex "testThisVertex" or current vertex. But in my result it ended looping and looping.

`int graph[HEIGHT][WIDTH]` is a 2 dimensional array, it's not an `int **link` array of pointers. There is a huge difference. And compiler should warn you about it. `graph[a][b]` is equal to `*(graph + a * WIDTH + b)` while `link[a][b]` is equal to `*(*(link + a) + b)` — KamilCuk, Jan 09 '19 at 11:02
Sorry, I edited again the function change to link[HEIGHT][WIDTH] — Anthony Gladiator, Jan 09 '19 at 11:14
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bruno · Answer 1 · 2019-01-09T11:35:00.420

lowest_label does not return a value in all the cases because of the else break; in the while

Finaly after some recursive calls with access to non initialized values and invalid accesses out of link and visitedLabelCheck there is a crash in if(link[currentLabel][currentCounter] != 0) because currentLabel values 1991084090`

I encourage you to compile with warning, if I use gcc with the options -pedantic -Wall the compiler indicates the missing return in lowest_label (and more)

How to do recursion on multidimensional array

1 Answers1