#0115

Number of Islands

MediumDSA25 min20 XP

Problem

Given a grid of "1" land and "0" water, return the number of islands using 4-directional connectivity.

Why This Matters

Grid connected-components problems are graph traversal in disguise.

Function Signature

def num_islands(grid):

Examples

Example 1

Input[["1","1","0"],["0","1","0"],["1","0","1"]]

Output3

The top-left connected land is one island; the two isolated cells are separate islands.

Constraints

Return the requested value exactly.
Handle the stated edge cases.
Keep the solution readable.

CodePython

def num_islands(grid):
    """
    Input example: [["1","1","0"],["0","1","0"],["1","0","1"]]
    Return: 3
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

def num_islands(grid):
    """
    Input example: [["1","1","0"],["0","1","0"],["1","0","1"]]
    Return: 3
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Input[["1","1","0"],["0","1","0"],["1","0","1"]]

Expected3

The top-left connected land is one island; the two isolated cells are separate islands.

Hidden Test Categories

all waterall landempty grid