Question Set 3 (10Q)

Author: Rudra-G-23

005_Problem_Sloving_with_Python/Q-03/01.py

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+""" 
+Write a function named first_non_repeating_char
+that returns the first character that does not
+repeat in a string. Return None if none exists.
+"""
+
+def first_non_repeating_char(text):
+    ch_dict = {}
+    
+    for ch in text:
+        if ch in ch_dict:
+            ch_dict[ch] += 1
+        else:
+            ch_dict[ch] = 1
+    
+    for ch in text:
+        if ch_dict[ch] == 1:
+            return ch
+ 
+    return None
+    
+
+print(first_non_repeating_char("swiss")) # 'w'
+print(first_non_repeating_char("aabbcc")) # None
+print(first_non_repeating_char("")) # None

005_Problem_Sloving_with_Python/Q-03/02.py

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+""" 
+Write a function named is_balanced_parenthese
+that checks if a string of parentheses is balanced.
+
+Rules
+- Every ( must have a matching )
+- Closing brackets must come after opening ones
+
+Stack style thinking+
+"""
+
+def is_balanced_parentheses(text):
+    count = 0
+    
+    for ch in text:
+        if ch == "(":
+            count += 1
+        else:
+            count -= 1
+        
+        if count < 0:
+            return False
+    
+    return count == 0
+                
+
+print(is_balanced_parentheses("(()())")) # True
+print(is_balanced_parentheses("(()")) # False
+print(is_balanced_parentheses(")(")) # False
+print(is_balanced_parentheses("")) # True

005_Problem_Sloving_with_Python/Q-03/03.py

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+""" 
+Rotate List to the Right
+
+Assumptions
+- nums is a list of integers
+- k is a non-negative integer
+- If k is greater than length of list → handle it properly
+- If list is empty → return empty list
+- Do NOT use any external libraries
+
+ex- 
+nums = [1, 2, 3, 4, 5], k = 2 -> [4, 5, 1, 2, 3]
+nums = [10, 20, 30], k = 4 -> [30, 10, 20]
+
+"""
+
+def rotate_right(nums, k):
+    if not nums:
+        return []
+    
+    k = k % len(nums)
+    return nums[-k:] + nums[:-k]
+
+print(rotate_right([1, 2, 3, 4, 5], 2))
+print(rotate_right([10, 20, 30], 4))
+print(rotate_right([], 3))

005_Problem_Sloving_with_Python/Q-03/04.py

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+""" 
+Rotate Left
+
+Constraints:
+- Do NOT use slicing (nums[a:b])
+- Do NOT create a second full list
+- Try to modify using loops
+"""
+
+def rotate_left(nums, k):
+
+    for i in range(len(nums)):
+        if i < k:
+            nums.append(nums[i])
+    for i in range(k-2):
+        nums.pop(i)
+            
+    return nums
+
+def rotate_left(nums, k):
+    n = len(nums)
+    if n == 0:
+        return nums
+    
+    k = k % n
+    
+    # Reverse first k
+    reverse(nums, 0, k - 1)
+    
+    # Reverse rest
+    reverse(nums, k, n - 1)
+    
+    # Reverse whole list
+    reverse(nums, 0, n - 1)
+    
+    return nums
+
+def reverse(nums, start, end):
+    while start < end:
+        nums[start], nums[end] = nums[end], nums[start]
+        start += 1
+        end -= 1
+
+print(rotate_left([1,2,3,4,5], 2)) # [3,4,5,1,2]

005_Problem_Sloving_with_Python/Q-03/05.py

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+""" 
+You are given a function that is
+supposed to count the frequency of
+each element in a list.
+"""
+
+def count_frequency(nums):
+    freq = {}
+    
+    for i in range(len(nums)):
+        if nums[i] in freq:          
+            freq[nums[i]] += 1
+        else:
+            freq[nums[i]] = 1
+    
+    return freq
+
+print(count_frequency([1, 2, 2, 3, 1, 1]))

005_Problem_Sloving_with_Python/Q-03/06.py

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+""" 
+This function is supposed to
+find the maximum number in a list.
+"""
+
+def find_max(nums):
+    max_num = nums[0]
+    
+    for num in nums:
+        if num > max_num:
+            max_num = num
+            
+    return max_num
+
+print(find_max([-2, -5, -12, -8]))

005_Problem_Sloving_with_Python/Q-03/07.py

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+""" 
+This function is supposed to reverse a string.
+Don't used the slicing [::-1]
+"""
+
+def reverse_string(s):
+    
+    result = ""
+    
+    for i in range(len(s)-1, -1, -1):
+        
+        result = result + s[i]
+        
+    return result
+
+print(reverse_string("hello"))

005_Problem_Sloving_with_Python/Q-03/08.py

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+""" 
+This function is supposed to check if a string is a palindrome
+(A palindrome reads the same forward and backward)
+"""
+
+def is_palindrome(s):
+    for i in range(len(s)//2):
+        if s[i] != s[len(s)-1-i]:
+            return False
+    return True
+
+print(is_palindrome("madam"))

005_Problem_Sloving_with_Python/Q-03/09.py

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+""" 
+Write a function to remove duplicates
+from a list WITHOUT using set()
+Input:  [1, 2, 2, 3, 1, 4]
+Output: [1, 2, 3, 4]
+"""
+
+def remove_duplicates(list):
+    new_list = []
+    
+    for i in list:
+        if i not in new_list:
+            new_list.append(i)
+    return new_list
+
+print(remove_duplicates([1, 2, 3, 4, 1, 4]))
+
+# Method 2
+
+def remove_duplicates(nums):
+    seen = {}
+    result = []
+    
+    for num in nums:
+        if num not in seen:
+            seen[num] = True
+            result.append(num)
+            
+    return seen, result
+
+print(remove_duplicates([1, 2, 3, 4, 1, 4]))

005_Problem_Sloving_with_Python/Q-03/10.py

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+""" 
+Find the first non-repeating character in a string
+Input:  "aabbcde"
+Output: "c"
+"""
+
+def first_non_repeating_chr(chr):
+    string_set = {}
+    
+    for i in chr:
+        if i not in string_set:
+            string_set[i] = 1
+        else:
+            string_set[i] += 1
+            
+    for i in chr:
+        if string_set[i] == 1:
+            return i
+    
+    return None
+
+print(first_non_repeating_chr("aabbcde"))