/**
 * @param {number[][]} mat
 * @return {number[][]}
 */
 var updateMatrix = function (mat) {
  let row = mat.length, col = mat[0].length
  let dist = Array.from(Array(row), item => new Array(col).fill(0))
  let visited = Array.from(Array(row), item => new Array(col).fill(0))
  let queue = []
  // 将所有的 0 添加进初始队列中
  for (let i = 0; i < row; ++i) {
      for (let j = 0; j < col; ++j) {
          if (mat[i][j] == 0) {
              queue.push([i, j])
              visited[i][j] = true
          }
      }
  }

  let dirs = [
      [1, 0],
      [-1, 0],
      [0, 1],
      [0, -1],
  ]
  // 广度优先搜索
  while (queue.length !== 0) {
      let cell = queue.shift()
      let i = cell[0], j = cell[1]
      for (let dir of dirs) {
          let ii = i + dir[0]
          let jj = j + dir[1]
          if (ii >= 0 && ii < row && jj >= 0 && jj < col && visited[ii][jj] !== true) {
              dist[ii][jj] = dist[i][j] + 1
              queue.push([ii, jj])
              visited[ii][jj] = true
          }
      }
  }

  return dist
};