Add interview questions

algorithms/array.md

@@ -7,7 +7,7 @@ Arrays
 - Paginate an array with constraints, such as skipping certain items.
 - Implement a circular buffer using an array.
 - Given array of arrays, sort them in ascending order.
-- Given an array of integers, print out a histogram of using said array; include a base layer (all stars)
+- Given an array of integers, print out a histogram using the said array; include a base layer (all stars)
   - E.g. `[5, 4, 0, 3, 4, 1]`
 
 ```

questions/01-histogram-stars.md

@@ -0,0 +1,37 @@
+---
+id: 1
+title: Histogram Stars
+topics: [array]
+difficulty: easy
+---
+
+## Question
+
+```
+'''
+Given an array of integers, print out a histogram using the array. Include a base layer (all stars)
+
+[5, 4, 0, 3, 4, 1] will result in the following:
+
+******
+*****
+*
+****
+*****
+**
+'''
+```
+
+## Follow Up
+
+```
+Print out a vertical version of the histogram.
+
+*
+**  *
+** **
+** **
+** ***
+******
+'''
+```

questions/02-matrix-islands.md

@@ -0,0 +1,56 @@
+---
+id: 2
+title: Matrix Islands
+topics: [array, depth-first-search, matrix]
+difficulty: easy
+source:
+  - https://leetcode.com/problems/number-of-islands/
+  - https://leetcode.com/problems/max-area-of-island/
+  - https://leetcode.com/problems/number-of-distinct-islands/
+---
+
+## Question
+
+```
+'''
+Given a matrix of 0s and 1s, count the number of islands present.
+
+[[0,0,1],
+ [0,0,0],
+ [0,1,1]]
+
+Answer: 2
+'''
+```
+
+## Follow Up
+
+```
+Given a matrix of 0s and 1s, find the size of the largest island present.
+
+'''
+[[0,0,1],
+ [0,0,0],
+ [0,1,1]]
+
+Answer: 2
+```
+
+## Follow Up II
+
+```
+Given a matrix of 0s and 1s, find the number of unique islands present present.
+
+'''
+[[1,0,1,0],
+ [1,0,0,0],
+ [0,1,1,0]]
+
+Answer: 3
+
+[[1,1,0,1],
+ [0,0,0,0],
+ [0,1,1,0]]
+
+Answer: 2
+```

questions/03-k-smallest-two-sorted.md

@@ -0,0 +1,40 @@
+---
+id: 3
+title: K Smallest Elements from Two Sorted Arrays
+topics: [array]
+difficulty: easy
+---
+
+## Question
+
+```
+'''
+Find the k smallest elements from two sorted arrays of integers.
+
+Input: [1, 2, 3, 4, 5], [2, 3, 4], k = 3
+Output: [1, 2, 2]
+'''
+```
+
+## Time Complexities
+
+- Bad:
+  - Time: O((n + m)log(n + m))
+- Good:
+  - Time: O(k)
+
+## Sample Answers
+
+```py
+def k_smallest(A, B, k):
+  res = []
+  a = b = 0
+  while a < len(A) and b < len(B) and (a + b) < k:
+    if A[a] < B[b]:
+      res.append(A[a])
+      a += 1
+    else:
+      res.append(B[b])
+      b += 1
+  return res + A[a:k - b] + B[b:k - a]
+```

questions/04-synonyms.md

@@ -0,0 +1,36 @@
+---
+id: 4
+title: Synonyms
+topics: [graph]
+difficulty: medium
+---
+
+## Question
+
+```
+'''
+Given a list of synonym pairs, determine if two words are synonymous.
+Synonyms have a symmetric and transitive relation. i.e. if a <-> b and b <-> c, a <-> c.
+
+Input:
+[["computer", "laptop"]]
+"computer"
+"laptop"
+
+Output: true
+
+Input:
+[["computer", "laptop"], ["laptop", "pc"]]
+"computer"
+"pc"
+
+Output: true
+
+Input:
+[["computer", "laptop"], ["laptop", "pc"], ["tablet", "iPad"]]
+"computer"
+"iPad"
+
+Output: false
+'''
+```

questions/05-longest-consecutive-set-of-numbers.md

@@ -0,0 +1,33 @@
+---
+id: 5
+title: Longest Consecutive Set of Numbers
+topics: [graph]
+difficulty: hard
+source: https://leetcode.com/problems/longest-consecutive-sequence/
+---
+
+## Question
+
+```
+'''
+Given an array of integers, find the size of the largest set of consecutive numbers present in the array.
+
+Input: [100, 4, 200, 1, 3, 2]
+Output: 4 because {1, 2, 3, 4}
+'''
+```
+
+## Sample Answers
+
+```py
+def longest_consecutive(nums):
+    nums = set(nums)
+    best = 0
+    for x in nums:
+        if x - 1 not in nums:
+            y = x + 1
+            while y in nums:
+                y += 1
+            best = max(best, y - x)
+    return best
+```

questions/06-string-compression.md

@@ -0,0 +1,25 @@
+---
+id: 6
+title: String Compression and Decompression
+topics: [string]
+difficulty: easy
+---
+
+## Question
+
+```
+'''
+Given a string, compress it by grouping repeated characters. The length after
+compression must always be smaller than or equal to the original string.
+
+'aaabbccc' => 'a3b2c3'
+'''
+```
+
+```
+'''
+Given the above compressed string, decompress to obtain the original string.
+
+'a3b2c3' => 'aaabbccc'
+'''
+```

questions/07-biggest-number-after-swap.md

@@ -0,0 +1,21 @@
+---
+id: 7
+title: Biggest Number After Swap
+topics: [math]
+difficulty: medium
+source: https://leetcode.com/problems/maximum-swap/
+---
+
+## Question
+
+```
+'''
+Given a non-negative integer, find the maximum possible number if you can swap two digits at most once.
+
+2736 => 7236
+'''
+```
+
+## Follow Up
+
+- What if the given integer can be negative?

questions/08-pivot-index.md

@@ -0,0 +1,19 @@
+---
+id: 8
+title: Pivot Index
+topics: [array]
+difficulty: easy
+source: https://leetcode.com/problems/find-pivot-index/
+---
+
+## Question
+
+```
+'''
+Given an array of integers, return the pivot index of this array.
+
+A pivot index is the index where the sum of the numbers to its left is equal to the sum of the numbers to its right:
+
+[7, 2, 3, 4] => 1
+'''
+```

questions/09-move-zeroes.md

@@ -0,0 +1,18 @@
+---
+id: 9
+title: Move Zeroes
+topics: [array]
+difficulty: easy
+source: https://leetcode.com/problems/move-zeroes/
+---
+
+## Question
+
+```
+'''
+Given an array of integers, write a function to move all zeroes to the end of it while
+maintaining the relative order of the non-zero elements.
+
+[0, 1, 0, 3, 12] => [1, 3, 12, 0, 0].
+'''
+```