Winter vacation daily question - lucky numbers in the matrix

• Topic link ：https://leetcode-cn.com/problems/lucky-numbers-in-a-matrix/
• Title Description

 To give you one  m * n  Matrix , The number in the matrix   Each are not identical  . Please press   arbitrarily   Return all the lucky numbers in the matrix in order .

 Lucky number refers to the elements in the matrix that meet the following two conditions at the same time ：

 The smallest of all elements in the same row 
 The largest of all elements in the same column 

• Example

 Input ：matrix = [[3,7,8],[9,11,13],[15,16,17]]
 Output ：[15]
 explain ：15  Is the only lucky number , Because it is the smallest value in its row , It is also the maximum value in the column .

Ideas

Preprocessing with two arrays , Store the minimum value of each row and the maximum value of each column respectively . Then find the same value in the two arrays .

• Code

public List<Integer> luckyNumbers (int[][] matrix) {
    
    int m = matrix.length;
    int n = matrix[0].length;
    int[] rows = new int[m];
    int[] cols = new int[n];
    Arrays.fill(rows,Integer.MAX_VALUE);
    for (int i = 0; i < m; i++) {
    
        for (int j = 0; j < n; j++) {
    
            rows[i] = Math.min(rows[i],matrix[i][j]);
            cols[j] = Math.max(cols[j],matrix[i][j]);
        }
    }
    List<Integer> list = new ArrayList<>();
    for (int i = 0; i < m; i++) {
    
        for (int j = 0; j < n; j++) {
    
            if (cols[j]==rows[i])
                list.add(rows[i]);
        }
    }
    return list;
}