add Top_K_Frequent_Elements

Author: kumailn

Python/Longest_Common_Subsequence.py

@@ -0,0 +1,14 @@
+# Question(#1143): Given two strings text1 and text2, return the length of their longest common subsequence.
+# Solution: Use the longest common susequence dynamic programming algorithm
+
+def longestCommonSubsequence(text1: str, text2: str) -> int:
+    grid = [[0 for _ in range(len(text2)+1)] for _ in range(len(text1)+1)]
+    
+    for i in range(1, len(text1)+1):
+        for j in range(1, len(text2)+1):
+            if text1[i-1] == text2[j-1]:
+                grid[i][j] = 1 + grid[i-1][j-1]
+            else:   
+                grid[i][j] = max(grid[i][j-1], grid[i-1][j])
+
+    return grid[-1][-1]

Python/Top_K_Frequent_Elements.py

@@ -0,0 +1,26 @@
+# Question(#347): Given a non-empty array of integers, return the k most frequent elements.
+# Solution: Use a counting sort to place the most frequent items into buckets, loop through the buckets backwards,
+#           (since the last bucket cooresponds to the most common item), add the items in the bucket to our result and decrement
+#           value of k by the amount of items in the bucket
+
+def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+    # Make an array with len(nums) + 1 positions, because the max frequency of any element 
+    # can coorespond to the len(nums) + 1 index.
+    buckets = [[] for _ in range(len(nums) + 1)]
+    result = []
+
+    # Save a number to the bucket which cooresponds to its frequency
+    for a, b in collections.Counter(nums).items(): buckets[b] += [a]
+
+    # Loop through the buckets backwards, since the ones at the end are the most frequent elements
+    for i in buckets[::-1]:
+        # If k becomes 0 or negative, we've found enough items
+        if k <= 0: return result
+
+        # If there's stuff in the current bucket, add that stuff to our result, and
+        # decrement k by the amount of things we just added
+        if i:
+            result += i
+            k -= len(i)
+
+    return result

README.md

@@ -30,6 +30,8 @@
 | Product of Array Except Self | 22 | [238](https://leetcode.com/problems/product-of-array-except-self) | Medium | Array | [Python](Python/Product_of_Array_Except_Self.py)|
 | Trapping Rain Water | 23 | [42](https://leetcode.com/problems/trapping-rain-water) | Hard | Array, Two Pointer | [Python](Python/Trapping_Rain_Water.py) |
 | Longest Consecutive Sequence | 24 | [128](https://leetcode.com/problems/longest-consecutive-sequence/) | Hard | Array | [Python](Python/Longest_Consecutive_Sequence.py) |
+| Top K Frequent Elements | 25 | [347](https://leetcode.com/problems/top-k-frequent-elements/) | Medium | Array, Counting Sort, Hashmap | [Python](Python/Top_K_Frequent_Elements.py) |
+
 
 ## 🧵 Strings
 | Title | Leetcode # | Difficulty | Tags | Solution |
@@ -143,6 +145,7 @@
 | Unique Paths | 4 | [62](https://leetcode.com/problems/unique-paths/) | Medium | Dynamic Programming, Top Down | [Python](Python/Unique_Paths.py) |
 | Delete Operation for Two Strings | 5 | [583](https://leetcode.com/problems/delete-operation-for-two-strings/) | Medium | Dynamic Programming | [Python](Python/Delete_Operation_for_Two_Strings.py) |
 | Edit Distance | 6 | [72](https://leetcode.com/problems/edit-distance/) | Hard | Dynamic Programming, Top Down | [Python](Python/Edit_Distance.py) |
+| Longest Common Subsequence | 7 | [1143](https://leetcode.com/problems/longest-common-subsequence/) | Hard | Dynamic Programming, Bottom Up | [Python](Python/Longest_Common_Subsequence.py) |
 
 
 ## 🎨 Design