Question

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

Answer 1

#include <stdio.h>

#define ROWS 4
#define COLS 5

#define MAX_VAL 1000  // Assumes matrix values are in range [0, 999]

int findCommonElementInMatrixRows(int matrix[][5], int rows, int cols) {
    int map[MAX_VAL] = {0};

    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 (int i = 0; i < MAX_VAL; i++) {
        if (map[i] == rows) {
            return i;
        }
    }

    return -1;
}

int main() {
    int matrix[][COLS] = {
        {1, 2, 3, 5, 36},
        {4, 5, 7, 9, 10},
        {5, 6, 8, 9, 18},
        {1, 3, 5, 8, 24}
    };

    int result = findCommonElementInMatrixRows(matrix, ROWS, COLS);
    if (result != -1) {
        printf("Common element in all rows: %d\n", result);
    } else {
        printf("No common element found in all rows.\n");
    }

    return 0;
}



/*
run:

Common element in all rows: 5

*/

 

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