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Micro-Drill #263 — Flood fill (DFS on grid)

Graph Exploration Target: 15s

Recursive DFS on a grid with bounds + color check. Same pattern for island counting, connected regions, etc.

def fill(grid, i, j, old, new):
    if i < 0 or i >= len(grid): return
    if j < 0 or j >= len(grid[0]): return
    if grid[i][j] != old: return
    grid[i][j] = new
    for di, dj in [(1,0),(-1,0),(0,1),(0,-1)]:
        fill(grid, i+di, j+dj, old, new)

Type it from memory. Go.

Practice Problems

• 733. Flood Fill
• 200. Number of Islands

Related Coding Drills

• Drill #100 — Flood fill Easy
• Drill #68 — Minimum path sum in grid Medium