Number of Closed Islands - Leetcode 1254 - Python

Solving leetcode 1254 - Number of Closed Islands, today's daily leetcode problem on April 5th.

0:00 - Read the problem
0:30 - Drawing Explanation
7:00 - Coding Explanation

leetcode 1254

#neetcode #leetcode #python

[ShikaIE]

Just fyi for others, be careful when visiting neighbors if your dfs return boolean instead of count like here.

E.g: boolean dfs(grid, r, c) {
…code here..
return dfs(grid, r+1, c) &&
dfs(grid, r-1, c) &&
..the rest here..;
}

Doing this way will make you stop early and only half the island is visited. When the main for loop reach the unvisited part of the island again, the result will be wrong.

[schrodingerskatt]

If I'm able to make it to MAANG or any big tech, it would be only because of you Navi. Thankyou so much, I learn a lot from your channel.

[Andrew-ddvf]

You can alternatively use the bitwise AND operator (&) to combine the dfs statements, assuming it returns False when OOB and True otherwise.
Reason: if using "and", once you encounter the first dfs statement and it's false, the remaining dfs statements won't be executed (short-circuit), which will misrepresent the visited grids in future iterations of grid.

[JameS]

Awesome explaination as always NEET yor are GOAT of LeetCode

[ameyakhot.official]

We can also run the loop from 1 to row_len - 1 and 1 to col_len - 1. Because the land cells in the boundary are never going to be a part of the enclosed islands since minimum one side is boundary.

[alexsinx]

I just don't get why the time complexity is only O(n*m) once you have two nested for loops and additional recursive calls inside of them, wouldn't you have to consider the time complexity of the recursive calls either?

[vaibhavjade]

what about the case when there's water inside the land? we're exiting in that case and will run remaining set of land points, resulting in 2 counts for same island?

[MP-nyep]

This solution was so perfectly explained. Thank you.

[vishnuvardhan]

I like this person, because he is not a human being 😅😅😅HE REALLY FROM ALIENS 👽👽👽 WORLD 😅😅😅😊😊😊😊(REASON: IF I WATCH SAME PROBLEM IN OTHERS YOUTUBE CHANNES LIKE 10000 TIMES I CANT ABLE TO UNDERSTAND, SO ALIENS ONLY CREATE WONDERS).SIR PLEASE SUGGEST ME HOW TO BECOME LIKE YOU???
DEFINITELY HARDWORK MATTERS, OTHER THAN THESE??

[goshua]

Couldn’t you also have your for loops start from, 1, ROWS -1 so you don’t check the borders?

[MayankLC]

i just watched 5 mins and coded by myself .. and I did it :)

[vixguy]

Hi NeetCode!
I tried the same thing but I used true and false instead of 0s and 1s. I have no idea why this turns out to not work for a few testcases.

[akarsan]

Great work on the videos and explanation!!

[haard_]

Are cpp codes also available? If it s, can you share the same.

[julianelmasry]

For the Dfs could you also use booleans and just return Dfs in all directions using and?

[ssss-mvdx]

Why are we returning true for 1 which is not on the boundary?

[gnidnert]

can someone pls explain why do we return true if we have already visited (r, c) in the base case?

[harshitpant]

can someone explain what are we doing here: res += dfs(r, c)

[shubhangkhandelwal]

importance of (r, c) in visited in base case!!?

[midorukawa]

Thank you so much for this video, very helpful! :)
Just out of curiosity: is there a reason why ROWS and COLS are written in capitals? Is it a convention or just a personal choice?