I don't know why I am doing.

filt.cpp

#include <stdio.h>

int lowerBound(const int nums[], int numsSize, int target){
    int lb = 0, n = numsSize, step;
    
    while(n > 0){
        step = n/2;
        if(nums[lb+step] < target){
            lb += step+1;
            n -= step+1;
        } else {
            n = step;
        }
    }
    
    return lb ;
}

int upperBound(const int nums[], int numsSize, int target){
    int ub = 0, n = numsSize, step;
    
    while(n > 0){
        step = n/2;
        if(nums[ub+step] <= target){
            ub += step+1;
            n -= step+1;
        } else {
            n = step;
        }
    }
    
    return ub;
}

void printRange(int s, int e) {
    for(int i=s; i<=e; ++i)
        printf("%d ", i);
}

int main() {
    unsigned int a[20] = {1, 5, 9, 11, 18, 21, 23, 53, 200, 230, 330, 
                         331, 332, 333, 400, 401, 405, 430, 450, 480};
    int aSize = 20;
                         
    int b = 3;
    int al = lowerBound(a, aSize, b*100), ar = upperBound(a, aSize, b*100+99);
  
    /* all smaller/greater than a[] */
    if (al >= ar) printRange(b*100, b*100+99);
    else {
        printRange(b*100, a[al]-1);
        al++;
        while(al < ar) {
            printRange(a[al-1]+1, a[al]-1);
            al++;
        }
        printRange(a[al-1]+1, b*100+99);
    }

	return 0;
}