C Language Construction Hash Table solution LC majority Element problem

Leetcode on the majority element is the solution of the Time O (N), Space O (1).

https://leetcode.com/problems/majority-element/

Use hash table to solve the time O (n), space O (n). It is convenient to use HashMap in Java. A classmate asked how to use C language to construct hash table. I wrote one of them:

typedefstructNode {intVal, Count;} Node;typedefstructHASH {Node*NP; intsize, capacity;} HASH;#defineN 509#defineHash_val (N) Abs ((n)% n)Static intEnsurecapacity (HASH *hp) {    intsize, capacity; Node*NP; Size= hp->size; Capacity= hp->capacity; if(Size <capacity)return 0; if(Capacity = =0) Capacity=8; Elsecapacity<<=1; NP= (node*)realloc(HP-&GT;NP, capacity *sizeof(Node)); if(NP = =NULL)return-1; HP->capacity =capacity; HP-&GT;NP =NP; return 0;}Static voidFreehashtab (HASH htab[],intN) {    inti;  for(i =0; I < n; i++)        if(htab[i].np) Free(HTAB[I].NP); }intMajorityelement (intArr[],intN) {HASH htab[n],*HB; intI, J, cur, hval, res; memset (Htab,0+ I *sizeof(HASH));  for(i =0; I < n; i++) {cur=Arr[i]; Hval=hash_val (cur); HB= &Htab[hval];  for(j =0; J < hb->size; J + +)            if(Hb->np[j].val = =cur) Break; if(j = = Hb->size) {            if(Ensurecapacity (HB) = =-1)                Gotoerr; HB->np[j].val =cur; HB->np[j].count =1; HB->size++; } Else{HB->np[j].count++; }        if(Hb->np[j].count > N/2) {res= hb->Np[j].val;            Freehashtab (Htab, N); returnRes;    }} err:freehashtab (Htab, N); return-1; }

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The code is a little bit longer and there is definitely a bug. This time I ran into two questions:

1. When I expand the array, the code I started with is this:

    HP->NP = (node*)reallocsizeof(Node);     if (HP->NP = = NULL        ) return -1;

The problem here is that if realloc returns NULL, the original memory will not be erased. So here's a memory leak.

2. A hash function is required to map N to [0, N-1]. For a simple account, my hash function is simply defined as:

#define N 509#define hash_val (n) (n)% n

That's not right. Consider n = =-1, then the hash value is-1.

Again:

#define Hash_val (n) ABS (n)% n

It seems to be OK. But still does not, hehe, the test case on the LC is designed very well. Consider that n is-2147483648, then ABS (n) =-2147483648.

Note: 2147483648 exceeds the 32-bit int range, so abs (-2147483648) is undefined behavior.

Finally, replace the following:

#define Hash_val (N) Abs ((n)% n)

C Language Construction Hash Table solution LC majority Element problem