Binary search with returned index in STL?

Question

I need a binary search function.

I couldn\'t find any function in the standard library that will return the index of the found item, and if it wasn\'t found,

Answer 1

I'm quite certain the standard library doesn't include anything to do precisely what you're asking for.

To get what you want, you'll probably want to start from std::lower_bound or std::upper_bound, and convert the iterator it returns into an index, then complement the index of the value wasn't found.

Answer 2

int bin_search (ForwardIterator first, ForwardIterator last, const T& val)
{
  ForwardIterator low;
  low = std::lower_bound(first,last,val);
  if(low!=last && !(val<*low)){
    return (low - first + 1);
  }else{
    return 0;
  }
}

Answer 3

using STL we can find the index

vector<int> vec{1,2,3,4,5,6,7,8,9} ;
vector<int> :: iterator index;
index=lower_bound(vec.begin(),vec.end(),search_data);
return (index-vec.begin());

Answer 4

There is no simple STL method which returns index against a sorted vector as far as I know, however you can use sample function below:

/**
 * @param v - sorted vector instance
 * @param data - value to search
 * @return 0-based index if data found, -1 otherwise
*/
int binary_search_find_index(std::vector<int> v, int data) {
    auto it = std::lower_bound(v.begin(), v.end(), data);
    if (it == v.end() || *it != data) {
        return -1;
    } else {
        std::size_t index = std::distance(v.begin(), it);
        return index;
    }   
}

Answer 5

int a = 0, b = n-1;
while (a <= b) {
    int k = (a+b)/2;
    if (array[k] == x) 
    {
        // x found at index k
    }
    if (array[k] < x) a = k+1;
    else b = k-1;
}

Answer 6

Clearly, this "will return the bitwise complement" is a big deal for you and I do not understand what you mean. That said, lookup std::upper_bound and see if it does what you want.