First commit. Added problems 4, 6, 13, 20, 42.

Author: v0di

easy/13.py

@@ -0,0 +1,16 @@
+class Solution:
+    def romanToInt(self, s: str) -> int:
+        nums = {
+            'I':1, 'V':5, 'X':10, 'L':50,
+            'C':100, 'D':500, 'M':1000
+        }
+        integer = 0
+        for index in range(len(s)):
+            try:
+                if (n := nums[s[index]]) < nums[s[index+1]]:
+                    integer -= n
+                else:
+                    integer += n
+            except IndexError:
+                integer += n
+        return integer

easy/20.py

@@ -0,0 +1,11 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        close = {'(':')', '[':']', '{':'}'}
+        left = close.keys()
+        queue = []
+        for par in s:
+            if par in left:
+                queue.append(close[par])
+            elif not queue or par != queue.pop(): 
+                return False
+        return True if not queue else False

hard/4.py

@@ -0,0 +1,8 @@
+class Solution:
+    def findMedianSortedArrays(self, nums1: List[int], nums2: List[int]) -> float:
+        nums = sorted(nums1 + nums2)
+        size = len(nums)
+        half = nums[(size-1)//2]
+        if not size%2:
+            return (half + nums[(size)//2])/2
+        return half

hard/42.py

@@ -0,0 +1,13 @@
+class Solution:
+    def trap(self, height: List[int]) -> int:
+        if len(height) == 1: return 0
+        trapped = 0
+        maxLeft = height[0] 
+        maxRight = max(height[1:])
+        for idx in range(1, len(height) - 1):
+            if height[idx-1] > maxLeft: maxLeft = height[idx-1]
+            if height[idx] == maxRight: maxRight = max(height[(idx+1):])
+            y = min(maxLeft, maxRight) - height[idx]
+            if y > 0:
+                trapped += y
+        return trapped

medium/6.py

@@ -0,0 +1,10 @@
+class Solution:
+    def convert(self, s: str, numRows: int) -> str:
+        if numRows == 1: return s
+        rows = ['' for i in range(numRows)]
+        x, it = 0, -1
+        for char in s:
+            rows[x] += char
+            if not x%(numRows - 1): it = -it
+            x += it
+        return ''.join(rows)