Question

I have

Str A = "abcdef"
Str B = "abcdf"

I need a function(stA, stB) that returns 5 (ie. the number of characters matched), note that these characters need to be in same order.

For example:

Str A = "abcdef"
Str B = "fedcba",

function(stA, stB) would only return 1 for the ‘a’

Pseudo code is good…

Oh btw given that all my strings will have <= 40 characters, O(n^2) might even be better than a O(41n) algorithm..

Answer 1

I haven’t fully tested it, but this seems to be working (in JavaScript) for your test cases:

function compare(a, b)
{
    var aChars = a.split('');
    var bChars = b.split('');

    var matches = [];
    var bStart = 0;

    for (var i=0; i < aChars.length; i++)
    {
        for (var j=bStart; j < bChars.length; j++)
        {
            if(aChars[i] == bChars[j])
            {
                matches.push(aChars[i]);
                bStart = j;
                break;
            }
        }
    }

    return matches.length;
}

compare('abcdef', 'abcdf'); // returns 5
compare('abcdef', 'fedcba'); // returns 1

Basically I’m starting at position 0 for string A and position 0 for string B. When a match is found, I change the start position for searching string B so that it skips the previous section.