岛屿数量

    /** grid二维数组
    */
    var landCount = function (grid) {
      let count = 0
      function dfs(row,col) {
        if(row< 0 || row>=grid.length || col<0 || col>=grid[0].length || grid[row][col] === "0"){
          return 
        }
        grid[row][col] = "0"
        dfs(row-1,col)
        dfs(row+1,col)
        dfs(row,col-1)
        dfs(row,col+1)
      }
      for(let row = 0;row<grid.length;row++){
        for(let col = 0;col<grid[0].length;col++){
          if(grid[row][col] === "1"){
            count++
            dfs(row,col) //递归找四个方位是否为1 并沉没
          }
        }
      }
      return count
    }