SDE - 1

You are given an array 'ARR' of integers of length N. Your task is to find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can have negative numbers as well.

For example, the input [3, 4, -1, 1] should give output 2 because it is the smallest positive number that is missing in the input array.

Given a string input of length n, find the length of the longest substring without repeating characters i.e return a substring that does not have any repeating characters.

Substring is the continuous sub-part of the string formed by removing zero or more characters from both ends.

There is a person , and Infront of him there are 2 closed rooms and there is light in one room and switches in the other room . What is the minimum number of times he moves in between the both the rooms and on the light?

A milk man carries a full 12 litres container of milk, he needs to deliver exactly 6 litre milk to customer and the milk vendor has only 8litres and 5litres containers. How can he exactly measure 6 litres from the containers he had?