Program to find smallest intersecting element of each row in a matrix in Python

Suppose we have a 2D matrix where each row is sorted in ascending order. We have to find the smallest number that exists in every row. If there's no such result, then return −1.

So, if the input is like

then the output will be 5

To solve this, we will follow these steps −

• if matrix is empty, then

  • return −1

• first := a new set from first row of matrix

• for each row in matrix, do

  • first := Intersect first a set of elements of row

  • if first is empty, then

    • return −1

• return minimum of first

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution:
   def solve(self, matrix):
      if not matrix:
         return -1
      first = set(matrix[0])
      for row in matrix:
         first &= set(row)
         if not first:
            return -1
      return min(first)
ob1 = Solution()
matrix = [
   [2, 3, 5],
   [5, 10, 10],
   [1, 3, 5]
]
print(ob1.solve(matrix))

Input

matrix = [
[2, 3, 5],
[5, 10, 10],
[1, 3, 5] ]

Output

5

Arnab Chakraborty

Updated on: 21-Oct-2020

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