50235. Valid Variable Name

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

#define max(a,b) ((a)>(b)?(a):(b))

static inline int is_dig(char c){
    return c >= '0' && c <= '9';
}
static inline int is_alp(char c){
    return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
}
static inline int is_uds(char c){
    return c == '_';
}

int f(char* s){
    int cnt = 0;
    while(*s != '\0') cnt += (*s), s++;
    return cnt % 1000;
}
int is_valid(char* s){
    if(*s == '\0' || is_dig(*s)) return 0;

    while(*s != '\0'){
        if(is_alp(*s) || is_dig(*s) || is_uds(*s)) s++;
        else return 0;
    }
    return 1;
}

typedef struct{
    char* table[1000][3];
    int cnt[1000][3];
} hash_table;
void init_table(hash_table *h){
    memset(h->cnt, -1, sizeof(h->cnt));
}
int insert(hash_table *h, char *s){
    int key = f(s);

    int exact_idx = -1, first_blank = -1;
    for(int i = 0; i < 3; i++){
        if(first_blank == -1 && h->cnt[key][i] == -1){
            first_blank = i;
        }
        if(h->cnt[key][i] != -1 && strcmp(s, h->table[key][i]) == 0){
            exact_idx = i;
            break;
        }
    }

    if(exact_idx != -1){
        h->cnt[key][exact_idx]++;
        return h->cnt[key][exact_idx];
    }
    else{
        char* new_str = (char*) malloc(sizeof(char) * 22);
        strcpy(new_str, s);
        h->table[key][first_blank] = new_str;
        h->cnt[key][first_blank] = 1;
        return 1;
    }
}


int main(){
    char s[22];
    hash_table* h = (hash_table*) malloc(sizeof(hash_table));
    init_table(h);

    while(scanf("%s", s) != EOF){
        if(!is_valid(s)) continue;
        int rtv = insert(h, s);
        printf("%s %d\n", s, rtv);
    }
}