LeetCode: fault list

1. malloc memory should always use the following form:

int *a = malloc(sizeof(int) * 3);
int **b = malloc(sizeof(int*) * 3);
int i = 0;
for (; i < 3; i++) {
    b[i] = malloc(sizeof(int) * 3);
}
char *c = malloc(sizeof(char) * length);
char **pc = malloc(sizeof(char *) * 4);
for (i = 0; i < 4; i++) {
    pc[i] = malloc(sizeof(char) * 3);
}

2. memset memory to 0 should use the form:

// Using the malloced memory above:
memset(a, 0, sizeof(int) * 3);
memset(b, 0, sizeof(int*) * 3);
for (i = 0; i < 3; i++) {
    memset(b[i], 0, sizeof(int) * 3);
}
memset(c, 0, sizeof(char) * 3);
memset(pc, 0, sizeof(char *) * 4);
for (i = 0; i < 4; i++) {
    memset(pc[i], 0, sizeof(char) * 3);
}

3. malloc(0) might also return address which is non-null. Which is error-prone. Consider use the following malloc. (..my implementation, any suggestion?)

#define SMALLOC(x)       \
({                                  \
 void *addr;                      \
 if ((x) == 0)                  \
 addr = 0;                      \
 else addr = malloc(x);    \
 (addr);                          \
 })

4. assign value from variables of different types *NEEDS* explicit type conversion. (e.g. when using double pow(double, double)), because values of different type has different binary presentation.

int ret = 0;
ret = (int)pow( (double)2.0, (double)1);

5. when retrieving N's decimal digits, it is better to do as the following, rather than doing: N mod(i*=10), because when N is large enough, i might overflow:

int a[20];
memset(a, 0, sizeof(int)*20);
while (N) {
    a[i++] = N%10;
    N /= 10;
}

6. doing swap using xor should be careful when equals. (when eauals each is set 0)

int swap(int *x, int *y) {
    if (*x != *y) {
        *x = *x ^ *y;
        *y = *x ^ *y;
        *x = *x ^ *y;
    }
    return 0;
}