如何检查元素在矩阵（C）中是否存在多次？

Question

I'm studying C programming language, and I came across a question that I got stuck trying to solve. I tried searching for an answer to my question, but I couldn't find.

My question is how to check if an element exists more than once in a matrix. Also, if it exists more than once but in the same row, it doesn't count.

I tried writing a function to do this, but when I look at it I get a headache hehe, so I guess I did it all wrong from the start.

Can someone please tell me how to do it?

Thanks in advance.

Answer 1

1. Check if an element exists more than once in an matrix: Sort the whole array (as if it would be a single linear vector). Then go linear through the vector and check if neighbouring elements are the same.
2. Check if an element exists more than once in a column of a matrix: Do the same as in 1. but only for each column.

Answer 2

For what you ask, you need to analyze all the element in the matrix. You also need to keep track if the element was already found in that column. Here is a sample code:

int count(int **matrix, int rows, int cols, int number) {
  int count=0, found_in_row=0, i, j;
  for(i=0; i<rows; i++) {
    for(j=0; j<cols; j++) {
      if(matrix[i][j]==number && found_in_row==0) {
        count++;
      }
    }
    found_in_row=0;
  }
 return count;
}

Now suppose i have this matrix:

1 2 1
1 2 3

By calling count(matrix, 3, 3, 1) you will get 2 as answer. That mean that the number 1 occur two times (withount counting the second 1 on the first row). So, by calling count on you matrix you will know if number occur more than once by checking if is greater than 1.