题目：
题解：
type point struct{x, y int
}var dirs = []point{{-1, 0}, {1, 0}, {0, -1}, {0, 1}}func updateMatrix(mat [][]int) [][]int {var m, n = len(mat), len(mat[0])var res = make([][]int, m)var visited = make([][]bool, m)var queue []pointfor i := range mat{res[i] = make([]int, n)visited[i] = make([]bool, n)for j := range mat[i]{if mat[i][j] == 0 {queue = append(queue, point{i, j})visited[i][j] = true}}}for len(queue) != 0 {cur := queue[0]queue = queue[1:]for _, dir := range dirs{i, j := cur.x + dir.x, cur.y + dir.yif i >=0 && i < m && j >=0 && j < n && !visited[i][j]{res[i][j] = res[cur.x][cur.y] + 1queue = append(queue, point{i,j})visited[i][j] = true}}}return res
}