Problem

At Genexa Bio, a cell-based assay is represented as a 2D grid where each entry is either 1 (cell with a target phenotype) or 0 (non-target). Write a function to count how many distinct phenotype clusters appear in the grid.

A cluster is a group of horizontally or vertically adjacent 1s. Diagonal cells are not connected.

Formal Specification

• Input: A 2D list grid of integers where each value is 0 or 1
• Output: An integer representing the number of connected clusters of 1s

Examples

Example 1

Input: grid = [
  [1,1,0,0],
  [1,0,0,1],
  [0,0,1,1],
  [0,0,0,0]
]
Output: 2

Explanation: The top-left group forms one cluster, and the connected cells on the right form the second cluster.

Example 2

Input: grid = [
  [1,0,1],
  [0,0,0],
  [1,0,1]
]
Output: 4

Explanation: Each 1 is isolated, so each one forms its own cluster.

Constraints

• 1 <= len(grid) <= 300
• 1 <= len(grid[0]) <= 300
• grid[i][j] is either 0 or 1
• Use horizontal and vertical adjacency only