1380. Lucky Numbers in a Matrix

Problem Link

Description

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Given an m x n matrix of distinct numbers, return all lucky numbers in the matrix in any order.

A lucky number is an element of the matrix such that it is the minimum element in its row and maximum in its column.

 

Example 1:

Input: matrix = [[3,7,8],[9,11,13],[15,16,17]]
Output: [15]
Explanation: 15 is the only lucky number since it is the minimum in its row and the maximum in its column.

Example 2:

Input: matrix = [[1,10,4,2],[9,3,8,7],[15,16,17,12]]
Output: [12]
Explanation: 12 is the only lucky number since it is the minimum in its row and the maximum in its column.

Example 3:

Input: matrix = [[7,8],[1,2]]
Output: [7]
Explanation: 7 is the only lucky number since it is the minimum in its row and the maximum in its column.

 

Constraints:

• m == mat.length
• n == mat[i].length
• 1 <= n, m <= 50
• 1 <= matrix[i][j] <= 105.
• All elements in the matrix are distinct.

Solution

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C++

class Solution {
public:
    vector<int> luckyNumbers (vector<vector<int>>& matrix) {
        int rows = matrix.size(), cols = matrix[0].size();
        vector<int> rowMin(rows, INT_MAX), colMax(cols, INT_MIN);
        vector<int> res;
 
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                rowMin[i] = min(rowMin[i], matrix[i][j]);
                colMax[j] = max(colMax[j], matrix[i][j]);
            }
        }
 
        for (int i = 0; i < rows; i++)
            for (int j = 0; j < cols; j++)
                if (matrix[i][j] == rowMin[i] && matrix[i][j] == colMax[j]) {
                    res.push_back(matrix[i][j]);
                    break;
                }
 
 
        return res;
    }
};

Python3

class Solution:
    def luckyNumbers (self, matrix: List[List[int]]) -> List[int]:
        r,c = len(matrix), len(matrix[0])
        col = [0] * c
        # calculate max col
        for i in range(c):
            col[i] = max([matrix[j][i] for j in range(r)])
        
        res = []
        for i in range(r):
            for j in range(c):
                if min(matrix[i]) == matrix[i][j] and col[j] == matrix[i][j]:
                    res.append(matrix[i][j])
                
        return res