Server Cluster Count

medium

A datacenter rack map is a grid: "1" marks a powered server, "0" marks an empty slot. Servers that touch horizontally or vertically share a network segment and form one cluster.

Given the grid of strings rack, return the number of distinct clusters. Diagonal contact does not connect servers.

Example 1

in rack = [["1","1","0"],["0","1","0"],["0","0","1"]]

out 2

The three 1s in the top-left corner touch and form one cluster; the bottom-right 1 stands alone.

Example 2

in rack = [["0","0"],["0","0"]]

out 0

Constraints

· 1 <= rows, cols <= 12
· rack[r][c] is "0" or "1"