leetcode-1380-easy

Lucky Numbers in a Matrix

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.

思路一：m*n 的二维数组，先求出每个 m 的最小值，然后求每个 n 的最大值，如果最大值和最小值相等，就是所求解

public List<Integer> luckyNumbers (int[][] matrix) {
    int m = matrix.length;
    int n = matrix[0].length;

    int[] minVal = new int[m];
    for (int i = 0; i < matrix.length; i++) {

        int min = matrix[i][0];
        for (int j = 1; j < matrix[i].length; j++) {
            min = Math.min(min, matrix[i][j]);
        }
        minVal[i] = min;
    }

    int[] maxVal = new int[n];
    for (int i = 0; i < n; i++) {
        int max = Integer.MIN_VALUE;
        for (int j = 0; j < m; j++) {
            max = Math.max(max, matrix[j][i]);
        }
        maxVal[i] = max;
    }

    for (int k : minVal) {
        for (int i : maxVal) {
            if (k == i) {
                return new ArrayList<>(Arrays.asList(k));
            }
        }
    }

    return new ArrayList<>();
}