代码给出运行时错误？

Question

i am trying to solve leetcode question :-

https://leetcode.com/problems/largest-number/ Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330. i am trying to sort strings by defining comparator to compare strings by concatinating right-to-left or left-to-right.

The program is giving runtime error. Please help....

int comp(const void* a, const void* b){
        int p = *((int *)a);
        int q = *((int *)b);
        int size = 14;
        char * first = (char *)malloc(size * sizeof(char));
        char * second = (char *)malloc(size * sizeof(char));
        first[0] = "\0";
        second[0] = "\0";
        sprintf(first, "%d",p);
        sprintf(first, "%d",q);
        sprintf(second, "%d",q);
        sprintf(second, "%d",p);
        return -1*strcmp(first, second);
    }

    char* largestNumber(int* nums, int numsSize) {
        if(numsSize <=0)
            return NULL;
        qsort(nums, numsSize, sizeof(int), comp);
        char * result = (char*)malloc(numsSize *5*sizeof(char));
        int i;
        for(i=0; i<numsSize; i++)
            result = strcat(result, nums[i]);
        return result;
    }

Answer 1

• Allocating memory with malloc() and throwing it away is a bad practice. Since you always allocate fixed amount of memory in comp , use regular array.
• Don't do first[0] = "\\0"; , which is assigning an pointer to char variable. Also remove useless sprintf , whose result is soon be overwritten.
• Allocating 5 bytes for each elements may be too small if int has 4 bytes. Allocate more memory.
• Initialize the buffer pointed by result before passing it to strcat() .
• Convert the integer to string before passing it to strcat() .
• They say that you shouldn't cast the result of malloc() in C .

Possible fix (not tested):

int comp(const void* a, const void* b){
    int p = *((int *)a);
    int q = *((int *)b);
    char first[14];
    char second[14];
    sprintf(first, "%d", q);
    sprintf(second, "%d", p);
    return -1 * strcmp(first, second);
}

char* largestNumber(int* nums, int numsSize) {
    if(numsSize <= 0)
        return NULL;
    qsort(nums, numsSize, sizeof(int), comp);
    char * result = malloc(numsSize * 14 * sizeof(char));
    int i;
    result[0] = '\0';
    for(i = 0; i < numsSize; i++) {
        char num[14];
        sprintf(num, "%d", nums[i]);
        result = strcat(result, num);
    }
    return result;
}