题目：
题解：
var (dirs = [][]int{[]int{-1, 0}, []int{1, 0}, []int{0, -1}, []int{0, 1}}rows, columns int
)func longestIncreasingPath(matrix [][]int) int {if len(matrix) == 0 || len(matrix[0]) == 0 {return 0}rows, columns = len(matrix), len(matrix[0])outdegrees := make([][]int, rows)for i := 0; i < rows; i++ {outdegrees[i] = make([]int, columns)}for i := 0; i < rows; i++ {for j := 0; j < columns; j++ {for _, dir := range dirs {newRow, newColumn := i + dir[0], j + dir[1]if newRow >= 0 && newRow < rows && newColumn >= 0 && newColumn < columns && matrix[newRow][newColumn] > matrix[i][j] {outdegrees[i][j]++}}}}queue := [][]int{}for i := 0; i < rows; i++ {for j := 0; j < columns; j++ {if outdegrees[i][j] == 0 {queue = append(queue, []int{i, j})}}}ans := 0for len(queue) != 0 {ans++size := len(queue)for i := 0; i < size; i++ {cell := queue[0]queue = queue[1:]row, column := cell[0], cell[1]for _, dir := range dirs {newRow, newColumn := row + dir[0], column + dir[1]if newRow >= 0 && newRow < rows && newColumn >= 0 && newColumn < columns && matrix[newRow][newColumn] < matrix[row][column] {outdegrees[newRow][newColumn]--if outdegrees[newRow][newColumn] == 0 {queue = append(queue, []int{newRow, newColumn})}}}}}return ans
}
