Question

I have a vector<string> vectorStrings with values: ta, bc, ac, st, cer, cda. I want to find the first occurrence of any of the strings in the vector in an input string.

e.g.

InputStr = "this certainly helps";

Of the given strings in the vector, I would want a way to say "cer" was the first occurrence at position 5.

---

int min = 9999999;
string first;

for(int i = 0; i < vectorStrings.size(); i++)
{
    int pos = InputStr.find(vectorStrings[i]);

    if(pos == string::npos)
        continue;

    if(pos < min)
    {
        min = pos;
        first = vectorStrings[i];
    }
}

// values of min and first gives which string occurred first
// and at the position of it in the input string

This implementation works, but I would want to know if there exists a more elegant way to do this with boost libraries or std library.

I am working on Windows and using Visual Studio 2010.

Answer 1

This is a MapReduce problem.

First, you want to go from vector<string> to vector<int>, of their positions, which is a map, and then you want to reduce the values to one value by their minimum, which is a reduction. First, the map. This is std::transform.

std::vector<std::string> stuff;
std::string input;
// fill stuff and input
std::vector<int> positions;
std::transform(
    stuff.begin(), 
    stuff.end(), 
    std::back_inserter(positions), 
    [&](std::string& stuff) {
        return input.find(stuff);
    }
);

Now we simply use std::min_element to get the smallest element, the reduce.

auto iterator = std::min_element(positions.begin(), positions.end());
int index = *iterator;

To find the string that was found there, it’s a simple bit of iterator arithmetic:

string found = stuff[iterator - positions.begin()];