Time complexity

  • You can get it counting the number of operations
  • Time complexity is defined as a function using Big O notation.
  • n is the size of the input.
  • O is the worst case scenario.
  • The O function is the growth rate in function of the input size n.

O(1) Constant : odd or even / look up table / check if item in array is null / print first element from a list / find on a map.

O(log n) Logarithmic: find in sorted array with binary search.

O(n) Linear: find max in unsorted array / duplicate elements in array with Hash map / find / print all values.

Algorithms running times:

Factorial complexity(no good),

exponential complexity(no good),

polinomial complexity (no good),

linearithmic complexity (middle point),

linear time complexity (good)(for loop in one level array, searching, printing) O(n),

logarithmic complexity (good) O(log n),

constant time complexity (best one)(swap variables). O(1)

Time Conversion

Problem from Hackerranck.

I am practising algorithms and tried this one today.

I first get the two first characters of the string ‘s’, the ones that represent the hour and change them to a number with parseInt and assign them to the variable hour.

If this variable hour is bigger than 12 I rest 12, if it is equals 12, hour would be the string ’00’ and for the rest of the cases I add 12.

Then I add hour to a substring of the argument without the two first characters and delete the two last characters too, the one that should be “AM” or “PM”.

My solution:

BirthdayCakeCandles

ProblemĀ from Hackerrank.

My solution:

 

Mini-Max Sum

ProblemĀ from Hackerrank.

My solution:

 

Staircase

ProblemĀ from Hackerrank.

My solution:

 

Plus Minus

ProblemĀ from Hackerrank.

I was making the mistake of checking if the index was bigger or smaller than zero, instead of checking the value of the integer in that index. I was comparingĀ iĀ instead ,arr[i].

My solution:

 

Diagonal Difference

ProblemĀ from Hackerrank.

 

Simply Array Sum

Problem from HackerRank.

Easy problem but I got confused with the index of the array and its value. I was adding iĀ to my result variable and not ar[i].

 

Compare the Triplets

ProblemĀ from Hackerrank.

Got some issues figuring out why it didn’t work my function. Two mental notes:

I am still have some problems with indentation and that can cause to put my return value inside the for loop without noticing.

I keep writing the operator “+=” as “=+”. How annoying! I read a good article about it and I finally got it.

My solution: