First Missing Positive - Leetcode 41 - Python

0:00 - Read the problem
1:35 - Drawing Explanation
16:35 - Coding Explanation

leetcode 41

#sorted #array #python
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[ygwg]

In the first round, setting all values less than zero and greater than N with the default value N+1 simplifies the coding a lot.

[ZQutui]

Thanks for the content. It's the best channel with algorithm explanations. It is explained so clear

[igboman]

Do people figure these things out by intuition or by studying?

[touwmer]

Man, this is 1000 times better than the official solution from leetcode Premium.

[paularah]

I paused and solved this problem about 4 mins into the video. You have an amazing way of opening one's eyes to insights. Thanks for sharing your knowledge.

[ameyakale]

The logic used to solve this problem is just insane. I love it ♥ Great explanation!

[cedricchen]

This is the best solution and explanation I have ever found, I have been stuck in understanding index as a hash way, especially the “while” statement since I saw this question. And I harshly believe that the leetcode solution is not intuitive as it looks like

[manubachhal]

Finally found a best channel coding in phyton .

[Jul]

Best explanation I've found so far, thanks man

[vadimkokielov]

Thank you for all the good videos!
One optimization I happened to come across that you missed. Your output range is actually not the length of the array, but the count of positive numbers in it -- a value you can compute very easily in your first loop.

[allen]

Thank you.

For the edge case where the original value is a zero, in addition to setting something out of bounds, could we also just set it the actual value its represending? E.x. when 2 exists in [-1, 0, ... ], could we set it to -2? That way we dont change the values in our input array since 2 is marked as existing already at some other place.

[rentianxiang]

Thank you! you are just awesome, please post more leetcode videos before I get accepted by Microsoft :)

[frida]

Dude, I couldn't do this hard question before, so I practiced a lot of the other medium questions and watched your videos. Then, I came back to this problem, and ended up figuring this out by myself! TYSM!!!

[linli]

Today I solved this problem and another problem called game of live, these two problems are difficult to figure out a solution with optimal space complexity because we need to store 2 pieces of information in a single figure, which is quite counter-intuitive.

[ehabteima]

It's impossible to come to the optimized solution unless you know it before hand.

[MiguelLopez-xvgf]

Thanks so much! you made it clear and easy to understand.
One question, shouldn't like 8 be `if 1 <= abs(A[i]) <= len(A) :` instead?

[AsmaeMouradi]

Thank you so much for all those videos you are really helping me. Waiting for more videos :)

[lonenrd]

Awesome explanation, I made a few modifications
def first_positive(nums):
n = len(nums)
for i in range(n):
if nums[i] < 1 or nums[i] > n:
nums[i] = n+1

for i in range(n):
if abs(nums[i]) > 0 and abs(nums[i]) <= n:
if nums[abs(nums[i]) -1] > 0:
nums[abs(nums[i]) -1] *= -1

for i in range(n):
if nums[i] > 0:
return i+1

return n+1

[Mr_SSK]

crisp and clear!
Thank you so much! :)

[soumyadeepganguly]

Beautifully done. I did it with a cycle sort type of method it got accepted but wasn't feeling good since it wasn't an O(n) solution. Got relief finally