Question

How to find a common element in all rows of a given matrix with sorted rows in C++

Answer 1

#include <unordered_map>
#include <iostream>
#include <vector>

int findCommonElementInMatrixRows(const std::vector<std::vector<int>> &matrix) {
    int rows = matrix.size();
    if (rows == 0) return -1; // Handle empty matrix
    int cols = matrix[0].size();

    std::unordered_map<int, int> map;
    
    for (int i = 0; i < rows; i++) {
        map[matrix[i][0]]++;
        for (int j = 1; j < cols; j++) {
            if (matrix[i][j] != matrix[i][j - 1]) {
                map[matrix[i][j]]++;
            }
        }
    }
   
    for (auto element : map) {
        if (element.second == rows) {
            return element.first;
        }
    }
    
    return -1;
}

int main() {
    // Example matrix with sorted rows
    std::vector<std::vector<int>> matrix = {
        {1, 2, 3, 5, 36},
        {4, 5, 7, 9, 10},
        {5, 6, 8, 9, 18},
        {1, 3, 5, 8, 24}
    };

    int result = findCommonElementInMatrixRows(matrix);
    if (result != -1) {
        std::cout << "Common element in all rows: " << result << std::endl;
    } else {
        std::cout << "No common element found in all rows." << std::endl;
    }
}



/*
run:

Common element in all rows: 5

*/

 

70+ SQL courses for beginners and professionals