Question

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

Answer 1

function findCommonElementInMatrixRows(matrix) {
    const map = new Map();
    const rows = matrix.length;
    const cols = matrix[0].length;

    for (let i = 0; i < rows; i++) {
        map.set(matrix[i][0], (map.get(matrix[i][0]) || 0) + 1);
        for (let j = 1; j < cols; j++) {
        if (matrix[i][j] !== matrix[i][j - 1]) {
            const val = matrix[i][j];
            map.set(val, (map.get(val) || 0) + 1);
        }
    }
  }

  for (const [key, count] of map.entries()) {
    if (count === rows) {
        return key;
    }
  }

  return -1;
}

const matrix = [
  [1, 2, 3, 5, 36],
  [4, 5, 7, 9, 10],
  [5, 6, 8, 9, 18],
  [1, 3, 5, 8, 24]
];

const result = findCommonElementInMatrixRows(matrix);
if (result !== -1) {
    console.log(`Common element in all rows: ${result}`);
} else {
    console.log("No common element found in all rows.");
}


/*
run:

Common element in all rows: 5

*/

 

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