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Count rows in a matrix that consist of same element in C++
We are given a matrix consisting of integers. The goal is to find the number of rows in the matrix that have all identical elements in it.
If there is 5X4 matrix as shown −
| 1 | 5 | 1 | 3 | 1 |
| 1 | 1 | 1 | 1 | 1 |
| 5 | 3 | 2 | 3 | 5 |
| 7 | 7 | 7 | 7 | 7 |
The answer would be 2, row 1 (having all 1’s) and row 3 (having all 7’s) contain the same element.
Let us understand with examples.
Input
matrix = [ 1 1 1 1 ] [ 2 3 2 7 ] [ 3 3 3 3 ]
Output − Count of rows in a matrix that consist of same element are − 2
Explanation − Row 0 contains all 1’s and row 2 contains all 3s.
Input −
matrix = [ 1 2 3 4 ] [ 1 2 3 4 ] [ 1 2 3 4 ]
Output − Count of rows in a matrix that consist of same element are − 0
Explanation − All rows have different elements.
Approach used in the below program is as follows
We are taking the matrix in the form of a vector of vectors<int>. We will traverse each vector and create a set<int> for each row. Keep on inserting row elements to this set. In the end if this set has only 1 element (take set size). Then the current row has all the same elements.
Take the matrix as a vector < vector <int> > matrix and initialize it
Calculate size using matrix.size().
Function same_rows(vector<vector<int>> matrix, int size) takes the matrix and it’s size and returns the count of rows that have the same elements.
Take the initial count as 0.
Traverse the matrix using for loop. i=0 to i=size.
For each row traverse from j=0 to j<matrix[i].size().
Take a set<int> set_row for storing elements of current row.
Add elements to this set for current row using set_row.insert(matrix[i][j]).
At the end check the size of set_row. If it is 1 then this row has all the same elements. Increment count.
At the end of all iterations for all rows, return count as the final result.
Example
#include <bits/stdc++.h>
using namespace std;
int same_rows(vector> matrix, int size){
int count = 0;
for (int i = 0; i < size; i++){
set set_row;
for (int j = 0; j < matrix[i].size(); j++){
set_row.insert(matrix[i][j]);
}
int set_size = set_row.size();
if (set_size == 1){
count++;
}
}
return count;
}
int main(){
vector<vector<int>> matrix = {
{ 2, 2, 2, 2},
{ 5, 5, 5, 5 },
{ 2, 2, 2, 2 },
{5, 5, 5, 5}
};
int size = matrix.size();
cout<<"Count of rows in a matrix that consist of same element are: "<<same_rows(matrix, size);
return 0;
}Output
If we run the above code it will generate the following output −
Count of rows in a matrix that consist of same element are: 4
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