LeetCode知识点总结 - 1380

LeetCode 1380. Lucky Numbers in a Matrix

题目

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.

思路

先对每行找到最小值，再判断这个值是不是那一列里最大的。

答案

public List<Integer> luckyNumbers (int[][] matrix) {
        List<Integer> result = new ArrayList<Integer>();
        
        for (int row = 0; row < matrix.length; row++) {
            int minCol = minColInRow(matrix, row);
            int value = matrix[row][minCol];
            if (checkIfMaxInCol(matrix, minCol, value)) {
                result.add(value);
            }
        }
        
        return result;
    }
    
    private int minColInRow(int[][] matrix, int row) {
        int minIndex = 0, min = matrix[row][minIndex];
        for (int col = 1; col < matrix[row].length; col++) {
            if (matrix[row][col] < min) {
                min = matrix[row][col];
                minIndex = col;
            }
        }
        return minIndex;
    }
    
    private boolean checkIfMaxInCol(int[][] matrix, int col, int value) {
        for (int row = 0; row < matrix.length; row++) {
            if (matrix[row][col] > value) return false;
        }
        return true;
    }