[Hacker Rank] Interview Preparation Kit: Greedy Algorithms: Luck Balance.

Author: Gonzalo Diaz

docs/hackerrank/interview_preparation_kit/greedy_algorithms/luck-balance.md

@@ -0,0 +1,97 @@
+# [Greedy Algorithms: Luck Balance](https://www.hackerrank.com/challenges/luck-balance)
+
+- Difficulty:  `#easy`
+- Category: `#ProblemSolvingBasic`
+
+Lena is preparing for an important coding competition that is preceded
+by a number of sequential preliminary contests.
+Initially, her luck balance is 0.
+She believes in "saving luck", and wants to check her theory.
+Each contest is described by two integers, `L[i]` and `T[i]`:
+
+- `L[i]` is the amount of luck associated with a contest.
+If Lena wins the contest, her luck balance will decrease by `L[i]`;
+if she loses it, her luck balance will increase by `L[i]`.
+
+- `T[i]` denotes the contest's importance rating.
+It's equal to `1` if the contest is important, and it's equal to `0` if it's unimportant.
+
+If Lena loses no more than `k` important contests, what is the maximum amount
+of luck she can have after competing in all the preliminary contests?
+This value may be negative.
+
+## Example
+
+```text
+Contest     L[i]    T[i]
+1           5       1
+2           1       1
+3           4       0
+```
+
+If Lena loses all of the contests, her will be `5 + 1 +4 = 10`.
+Since she is allowed to lose  important contests,
+and there are only `2` important contests,
+she can lose all three contests to maximize her luck at `10`.
+
+If `k = 1`, she has to win at least  of the  important contests.
+She would choose to win the lowest value important contest worth `1`.
+Her final luck will be `5 + 4 - 1 = 8`.
+
+## Function Description
+
+Complete the luckBalance function in the editor below.
+
+luckBalance has the following parameter(s):
+
+- `int k`: the number of important contests Lena can lose
+- `int contests[n][2]`: a 2D array of integers where each `contests[i]`
+contains two integers that represent the luck balance and importance of the  contest
+
+## Returns
+
+- `int`: the maximum luck balance achievable
+
+## Input Format
+
+The first line contains two space-separated integers  `n` and `k`,
+the number of preliminary contests and the maximum number
+of important contests Lena can lose.
+
+Each of the next  lines contains two space-separated integers,
+`L[i]` and `T[i]`, the contest's luck balance and its importance rating.
+
+## Constraints
+
+- $ 1 \leq n \leq 100 $
+- $ 0 \leq k \leq N $
+- $ 1 \leq L[i] \leq 10^4 $
+- $ T[i] \isin \{0,1\} $
+
+## Sample Input
+
+```text
+STDIN       Function
+-----       --------
+6 3         n = 6, k = 3
+5 1         contests = [[5, 1], [2, 1], [1, 1], [8, 1], [10, 0], [5, 0]]
+2 1
+1 1
+8 1
+10 0
+5 0
+```
+
+## Sample Output
+
+```text
+29
+```
+
+## Explanation
+
+There are `n = 6` contests. Of these contests, `4` are important
+and she cannot lose more than  of them.
+Lena maximizes her luck if she wins the $ 3^{rd} $ important contest
+(where `L[i] = 1`) and loses all of the other five contests for a total
+luck balance of `5 + 2 + 8 + 10 + 5 - 1 = 29`.