LeetCode 1380: Lucky Numbers in a Matrix Solution

Master LeetCode problem 1380 (Lucky Numbers in a Matrix), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1380. Lucky Numbers in a Matrix

Easy

Array Matrix

Problem Explanation

Explanation

We will iterate through each cell in the matrix and check if it is a lucky number.
For each cell, we will find the minimum element in its row and the maximum element in its column.
If the current cell value is both the minimum in its row and the maximum in its column, it is a lucky number.
We will store all lucky numbers found in a list and return the list as the result.

Time Complexity: O(m * n) where m is the number of rows and n is the number of columns in the matrix. Space Complexity: O(1) excluding the output list.

Solution Code

import java.util.ArrayList;
import java.util.List;

class Solution {
    public List<Integer> luckyNumbers (int[][] matrix) {
        List<Integer> luckyNums = new ArrayList<>();
        
        for (int i = 0; i < matrix.length; i++) {
            int minRow = Integer.MAX_VALUE;
            int colIdx = -1;
            for (int j = 0; j < matrix[i].length; j++) {
                if (matrix[i][j] < minRow) {
                    minRow = matrix[i][j];
                    colIdx = j;
                }
            }
            
            int maxCol = matrix[i][colIdx];
            for (int k = 0; k < matrix.length; k++) {
                if (matrix[k][colIdx] > maxCol) {
                    maxCol = -1;
                    break;
                }
            }
            
            if (minRow == maxCol) {
                luckyNums.add(minRow);
            }
        }
        
        return luckyNums;
    }
}

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