Question

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

Answer 1

import Foundation

func findCommonElement(in matrix: [[Int]]) -> Int {
    let rows = matrix.count
    guard rows > 0 else { return -1 }

    let cols = matrix[0].count
    var freq: [Int: Int] = [:]

    for row in matrix {
        freq[row[0], default: 0] += 1
        for j in 1..<cols {
            if row[j] != row[j - 1] {
                freq[row[j], default: 0] += 1
            }
        }
    }

    for (key, count) in freq {
        if count == rows {
            return key
        }
    }

    return -1
}

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

let result = findCommonElement(in: matrix)
if result != -1 {
    print("Common element in all rows: \(result)")
} else {
    print("No common element found in all rows.")
}


/*
run:

Common element in all rows: 5

*/

 

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