1380. Lucky Numbers in a Matrix

Posted 2021-03-05 wentiliangkaihua

Given a m * 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]

 

Constraints:

• m == mat.length
• n == mat[i].length
• 1 <= n, m <= 50
• 1 <= matrix[i][j] <= 10^5.
• All elements in the matrix are distinct.

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

lucky number: 既是每行最小的数，也是每列最大的数

设置两个数组存放每行最小，和每列最大的数

比较，两者必须相等才是一个可能的解，加入list中