Merge two sorted arrays recursively

This is a discussion on Merge two sorted arrays recursively within the C Programming forums, part of the General Programming Boards category; Hi, the exercise is this: I got two sorted arrays (of any length) and I got to merge them into ...

  1. #1
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    Merge two sorted arrays recursively

    Hi, the exercise is this:
    I got two sorted arrays (of any length) and I got to merge them into a new array (of correct length, and still sorted), recursively.

    I solved the problem like this:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    void merge(int *v1, int *v2, int l1, int l2, int *v3);
    int *newArray(int n);
    
    int main (void) {
        int *v1, *v2, *v3;
        int i, l1, l2, l3;
    
        v1 = v2 = v3 = NULL;
    
        printf("Enter the numbers in increasing order.\n\n");
    
        printf("First's array length: ");
        do{
            scanf("%d", &l1);
        }while(l1 <= 0);
    
        v1 = newArray(l1);
    
        printf("\nSecond's array length: ");
        do{
            scanf("%d", &l2);
        }while(l2 <= 0);
    
        v2 = newArray(l2);
    
        l3 = l1 + l2;
    
        v3 = malloc(l3 * sizeof(int));
        if(!v3)
            return -1;
    
        merge(v1, v2, l1, l2, v3);
    
        printf("\nResult:\n");
        for(i=0; i<l3; ++i)
            printf("%d ", v3[i]);
    
        return 0;
    }
    
    void merge(int *v1, int *v2, int l1, int l2, int *v3){
        if(l1 && l2){ // verifying if both vectors got elements
            if(*v1 <= *v2){
                *v3 = *v1;
                merge(++v1, v2, --l1, l2, ++v3);
            }
            else{
                *v3 = *v2;
                merge(v1, ++v2, l1, --l2, ++v3); // notare ++v2 e --l2 e ++v3
            }
        }
    
        else if(l1){ // verifying if only v1 got elements
            *v3 = *v1;
            merge(++v1, v2, --l1, l2, ++v3);
        }
    
        else if(l2){ // verifying if only v2 got elements
            *v3 = *v2;
            merge(v1, ++v2, l1, --l2, ++v3);
        }
    }
    
    int *newArray(int n){
        int *v = NULL;
        int i;
    
        v = malloc(n * sizeof(int));
    
        if(!v)
            return NULL;
    
        for(i=0; i<n; ++i){
            printf("[%d]: ", i);
            scanf("%d", &v[i]);
        }
    
        return v;
    }
    My solution seems to work well. I only got a doubt about how I solved it, it is: is there a way to make it in the form "v3 = merge(parameters);" ?
    I would like to know if I can do it with returns... it would be a non-void function.

    Thanks
    Last edited by kr0n1x; 06-04-2012 at 09:55 AM.

  2. #2
    spurious conceit MK27's Avatar
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    Quote Originally Posted by kr0n1x View Post
    I would like to know if I can do it with returns... it would be a non-void function.
    I think that will be a little awkward, actually. What you have now is very clear; if it works, just leave it that way. Why do you think using the return value would represent an improvement?
    Last edited by MK27; 06-04-2012 at 10:30 AM.
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    Quote Originally Posted by MK27 View Post
    I think that will be a little awkward, actually. What you have now is very clear; if it works, just leave it that way. Why do you think using the return value would represent an improvement?
    A lot of the recursive functions I've been using have returns (for example those with trees and lists management). Since I was not able to make it with returns (in this exercise), I was curious to know if the reason was behind my lack of experience or if, as you said, it is actually better to make it without returns.
    If you say this is a good solution, it's ok to me xD

    Thanks!

  4. #4
    Master Apprentice phantomotap's Avatar
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    O_o

    A return value can be viewed as syntactic sugar. A reference parameter could always be added and used allowing the function to be `void'. That alone doesn't make one design better or worse.

    Soma

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    Conceptually, you should be returning the array. Unfortunately, C doesn't really let you do that (without a lot of memory overhead).

  6. #6
    Algorithm Dissector iMalc's Avatar
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    If you wanted to pass v3 out then you'd probably also want to avoid passing it in. Therefore you'd probably want to move the malloc inside the merge function. Then you'd probably end up making lots of malloc calls, possibly leak memory, or return a buffer that had been freed, and ultimately end up with a worse solution.
    You're probably best doing it as you have now. However I suggest using better variable names as that would make it easier to follow.
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