Find specific value in matrix algorithm

Question

I have this matrix and I want to find a algorithm that can find all values = 1 and give give me the count of how many there are.

My matrix look like this and have the size n x n:

Right now I don't know what kind of algorithm I have to use.

please clarify your question. Why dont you just iterate over all elements of the matrix and count the number of 1s? — Nikunj Banka, Apr 24 '14 at 08:49
If you look at the matrix the is some empty values i don't know how i deal with them! and the what kind of algorithm could i use for a matrix search? — Alexander Marcussen, Apr 24 '14 at 08:54
@user3322871 so your question is how you should deal with the input? and what is your input look like , an array of String or number or ...? — Pham Trung, Apr 24 '14 at 09:00
Why do empty values make any difference if you're just counting the 1s? — Bernhard Barker, Apr 24 '14 at 09:03
Yes how should i deal with it ? The only input or info i have is the above matrix. I only have to make some pseudo code — Alexander Marcussen, Apr 24 '14 at 09:03
@user3322871 so the input you have is an array of String? so my next question will be how do you know that an element in the matrix is 44 or 4, is there any limit like the element should be from 0 to 9? — Pham Trung, Apr 24 '14 at 09:08
@Pham Trung yes it an array of string!its 4 and not 44 and no limits — Alexander Marcussen, Apr 24 '14 at 09:11
@user3322871 I am confused, can you give me the link to the problem? so all the character '1' will be counted? or do you differentiate between 101 and 1 and 10? — Pham Trung, Apr 24 '14 at 09:14
@PhamTrung its obvoius from what he says. For 101 there are two `1`s. For 10 there is one `1`. — Tahlil, Apr 24 '14 at 09:17
@Tahlil because in the question , it mentions `values` not character. — Pham Trung, Apr 24 '14 at 09:21
@user3322871 so this should be more like how you can parse the String in your programming language :) — Pham Trung, Apr 24 '14 at 09:22
But he also said in previous comment that `yes it an array of string!its 4 and not 44` — Tahlil, Apr 24 '14 at 09:22

Tahlil · Answer 1 · 2014-04-24T09:39:19.723

1

If it is a parsing problem then,

int count = 0;
for(int i=0;i<n;i++)
{
    for(int j=0;j<n;j++)
    {
        if(isdigit(matrix[i][j] && matrix[i][j]!='0')
        {
            int sum = 0;
            int tenPower = 1;
            for(;j<n && isdigit(matrix[i][j];j++)
            {
                sum = sum*tenPower+(matrix[i][j]-48);
                tenPower*=10;
            }
            if(sum == 1)count++;
            j--; 
         }
     } 
 }
 printf("%d\n",count);

edited Apr 24 '14 at 09:39

answered Apr 24 '14 at 09:07

Tahlil

2,550
4
36
71

Are you sure the second approach is faster?The time complexity for the second approach is O((n^2)logn ) – Pham Trung Apr 24 '14 at 09:22
no, it's not 2*n(log n), because every time you sorted a row with n element, the time complexity is O(nlogn), and you have n rows, which result in n*O(nlogn), which is O(n^2logn) – Pham Trung Apr 24 '14 at 09:26
You can never do better than n^2, because the number of character is n^2, how do you solve this problem with reading less than n^2 characters? Please think more carefully about this – Pham Trung Apr 24 '14 at 09:27

Find specific value in matrix algorithm

1 Answers1