1380. Lucky Numbers in a Matrix #

Problem #

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.

Problem Summary #

Given an m * n matrix, all numbers in the matrix are distinct. Return all lucky numbers in the matrix in any order. A lucky number is an element in the matrix that satisfies both of the following conditions:

It is the minimum among all elements in the same row
It is the maximum among all elements in the same column

Solution Approach #

Find the lucky numbers in the matrix. Definition of a lucky number: it satisfies 2 conditions at the same time, being the minimum among all elements in the same row and the maximum among all elements in the same column.
Easy problem. Traverse the matrix according to the problem statement, and output the numbers that satisfy both conditions.

Code #


package leetcode

func luckyNumbers(matrix [][]int) []int {
	t, r, res := make([]int, len(matrix[0])), make([]int, len(matrix[0])), []int{}
	for _, val := range matrix {
		m, k := val[0], 0
		for j := 0; j < len(matrix[0]); j++ {
			if val[j] < m {
				m = val[j]
				k = j
			}
			if t[j] < val[j] {
				t[j] = val[j]
			}
		}

		if t[k] == m {
			r[k] = m
		}
	}
	for k, v := range r {
		if v > 0 && v == t[k] {
			res = append(res, v)
		}
	}
	return res
}