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Concept

Matrices

A grid is a graph · DFS the 4 neighbours
step 1 / 99
4 × 4 grid as a graph
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Flood DFS on a grid
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1dfs(r, c):
2    mark visited[r][c] = true
3    for (dr, dc) in [up, down, left, right]:
4        nr, nc = r+dr, c+dc
5        if out of bounds: skip
6        if visited[nr][nc]: skip
7        dfs(nr, nc)             // recurse
8    return                       // backtrack
9dfs(startR, startC)
state
  • rows4
  • cols4
  • neighbours4-directional

line 1A grid is just a graph in disguise. Each cell is a NODE, and the edges run to its four orthogonal neighbours: up, down, left, right. No diagonals. DFS on a grid is the same depth-first walk you already know — pick a start, dive into a neighbour, and keep diving until you hit a wall.