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Wednesday, January 30, 2013

Interesting problems from Facebook hackers cup

Hi friends,
Yesterday i participated on a coding contest.. Felt it is worth sharing :)
Hope you enjoy it too...........


When John was a little kid he didn't have much to do. There was no internet, no Facebook, and no programs to hack on. So he did the only thing he could... he evaluated the beauty of strings in a quest to discover the most beautiful string in the world.

Given a string s, little Johnny defined the beauty of the string as the sum of the beauty of the letters in it.

The beauty of each letter is an integer between 1 and 26, inclusive, and no two letters have the same beauty. Johnny doesn't care about whether letters are uppercase or lowercase, so that doesn't affect the beauty of a letter. (Uppercase 'F' is exactly as beautiful as lowercase 'f', for example.)

You're a student writing a report on the youth of this famous hacker. You found the string that Johnny considered most beautiful. What is the maximum possible beauty of this string?

The input file consists of a single integer m followed by m lines.

Your output should consist of, for each test case, a line containing the string "Case #x: y" where x is the case number (with 1 being the first case in the input file, 2 being the second, etc.) and y is the maximum beauty for that test case.

5 ≤ m ≤ 50
2 ≤ length of s ≤ 500

Example input

Good luck in the Facebook Hacker Cup this year!
Ignore punctuation, please :)
Sometimes test cases are hard to make up.
So I just go consult Professor Dalves

Example output

Case #1: 152
Case #2: 754
Case #3: 491
Case #4: 729
Case #5: 646



Your friend John uses a lot of emoticons when you talk to him on Messenger. In addition to being a person who likes to express himself through emoticons, he hates unbalanced parenthesis so much that it makes him go :(

Sometimes he puts emoticons within parentheses, and you find it hard to tell if a parenthesis really is a parenthesis or part of an emoticon.

A message has balanced parentheses if it consists of one of the following:
- An empty string ""
- One or more of the following characters: 'a' to 'z', ' ' (a space) or ':' (a colon)
- An open parenthesis '(', followed by a message with balanced parentheses, followed by a close parenthesis ')'.
- A message with balanced parentheses followed by another message with balanced parentheses.
- A smiley face ":)" or a frowny face ":("

Write a program that determines if there is a way to interpret his message while leaving the parentheses balanced.

The first line of the input contains a number T (1 ≤ T ≤ 50), the number of test cases. The following T lines each contain a message of length s that you got from John.

For each of the test cases numbered in order from 1 to T, output "Case #i: " followed by a string stating whether or not it is possible that the message had balanced parentheses. If it is, the string should be "YES", else it should be "NO" (all quotes for clarity only)

1 ≤ length of s ≤ 100

Example input

i am sick today (:()
hacker cup: started :):)

Example output
Case #1: NO
Case #2: YES
Case #3: YES
Case #4: YES
Case #5: NO



After sending smileys, John decided to play with arrays. Did you know that hackers enjoy playing with arrays? John has a zero-based index array, m, which contains n non-negative integers. However, only the first k values of the array are known to him, and he wants to figure out the rest.

John knows the following: for each index i, where k <= i < n, m[i] is the minimum non-negative integer which is *not* contained in the previous *k* values of m.

For example, if k = 3, n = 4 and the known values of m are [2, 3, 0], he can figure out that m[3] = 1.

John is very busy making the world more open and connected, as such, he doesn't have time to figure out the rest of the array. It is your task to help him.

Given the first k values of m, calculate the nth value of this array. (i.e. m[n - 1]).

Because the values of n and k can be very large, we use a pseudo-random number generator to calculate the first k values of m. Given non-negative integers a, b, c and positive integer r, the known values of m can be calculated as follows:
m[0] = a
m[i] = (b * m[i - 1] + c) % r, 0 < i < k

The first line contains an integer T (T <= 20), the number of test cases. This is followed by T test cases, consisting of 2 lines each. The first line of each test case contains 2 space separated integers, n, k (1 <= k <= 105, k < n <= 109). The second line of each test case contains 4 space separated integers a, b, c, r (0 <= a, b, c <= 109, 1 <= r <= 109).

For each test case, output a single line containing the case number and the nth element of m.

Example input

97 39
34 37 656 97
186 75
68 16 539 186
137 49
48 17 461 137
98 59
6 30 524 98
46 18
7 11 9 46

Example output

Case #1: 8
Case #2: 38
Case #3: 41
Case #4: 40
Case #5: 12

Saturday, January 26, 2013

Freeing your RAM

Hi friends,
I was working on a server and suddenly the machine seemed to kind of slow. I guessed that my RAM was full and checked it. And as i suspected its free memory was less. I was shocked just by seeing the total used memory, it was way too high. I tried to trace down the processes but nothing seemed to consume so much.

   So i was assuming that one of the open source application which i was using had some memory leakage. So i wanted to make an investigation on that. All my attempts were failure. So from the experiment i understood the following about memory management in linux.

1. When ever some process is executed after usage it is cached to local storage
2. And this cached memory is not freed automatically.

So i found it, that was the culprit. This cached memory is the one that was occupying the RAM and RAM appeared to be full. So now i would be sharing you the command that would clear the cached memory in RAM and gives your system some space to breathe.

Here it is,

# sync; echo 3 > /proc/sys/vm/drop_caches

Sunday, January 6, 2013

Getting more info on segmentation fault

Hi all,
This is just a very small post which might be useful to you.. Mostly when you develop some codes, especially in some native languages like C, C++, sometimes you face some error "Segmentation Fault (Core Dumped)". This post is all about how we get more info on this when you are working on Linux.

Has anyone wondered what is that called "Core Dumped" that appears after segmentation fault ? and where is it dumped ? :) It is not dumped anywhere unless you enable it.. So we shall learn how to enable it....

Step 1: Change your current directory to temp

# cd /tmp

Step 2: Enable core dump

# ulimit -c unlimited

Step 3: Execute your program in which you face segmentation fault

For example,

# /opt/myprogram.out

It produces,

Segmentation Fault (core dumped)

Thats it, now you have core dumped in /tmp/core file. You can open it with your favorite editor (I prefer vi editor, as other editors crash mostly when you open such binaries).

The file is a binary and it has more junk info.. parse through the file to check some errors somewhere..