leetcode questions added

Author: shushrutsharma

14. Questions/leetcode 01 - two sum.py

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+"""
+Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
+
+You may assume that each input would have exactly one solution, and you may not use the same element twice.
+
+You can return the answer in any order.
+
+Question: https://leetcode.com/problems/two-sum/
+
+"""
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        for i in range(len(nums)):
+            for j in range(i+1, len(nums)):
+                if nums[i] + nums[j] == target:
+                    return [i,j]
+        return []

14. Questions/leetcode 09 - palindrome number.py

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+"""
+Given an integer x, return true if x is palindrome integer.
+
+An integer is a palindrome when it reads the same backward as forward.
+
+For example, 121 is a palindrome while 123 is not.
+
+Question: https://leetcode.com/problems/palindrome-number/
+
+"""
+
+
+class Solution:
+    def isPalindrome(self, x: int) -> bool:
+        if x < 0:
+            return False
+        c = x
+        b = 0
+        
+        while c:
+            b = b * 10 + c % 10
+            c //= 10
+            
+        return b == x
+        

14. Questions/leetcode 13 - roman to integer.py

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+"""
+Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
+
+Symbol       Value
+I             1
+V             5
+X             10
+L             50
+C             100
+D             500
+M             1000
+For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.
+
+Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:
+
+I can be placed before V (5) and X (10) to make 4 and 9. 
+X can be placed before L (50) and C (100) to make 40 and 90. 
+C can be placed before D (500) and M (1000) to make 400 and 900.
+Given a roman numeral, convert it to an integer.
+
+Questions: https://leetcode.com/problems/roman-to-integer/
+
+"""
+
+
+class Solution:
+    def romanToInt(self, s: str) -> int:
+        roman = {'I':1, 'V':5, 'X': 10, 'L':50, 'C':100, 'D':500, 'M':1000}
+        
+        res = 0
+        
+        for i in range(len(s)):
+            if i+1 <len(s) and roman[s[i]] < roman[s[i+1]]:
+                res = res - roman[s[i]]
+            else:
+                res = res + roman[s[i]]
+        return res

14. Questions/leetcode 14 - longest common prefix.py

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+"""
+Write a function to find the longest common prefix string amongst an array of strings.
+
+If there is no common prefix, return an empty string "".
+
+Questions: https://leetcode.com/problems/longest-common-prefix/
+
+"""
+
+class Solution:
+    def longestCommonPrefix(self, strs: List[str]) -> str:
+        res = ""
+        n = len(strs)
+        strs.sort()
+        first = strs[0]
+        last = strs[n-1]
+        for i in range(len(first)):
+            if first[i] != last[i]:
+                return res
+            else:
+                res = res + first[i]
+        return res
+        
+        
+        
+#         for i in range(len(strs[0])):
+#             for s in strs:
+#                 if i == len(s) or s[i] != strs[0][i]:
+#                     return res
+                
+#             res += strs[0][i]
+            
+#         return res

14. Questions/leetcode 20 - valid parentheses.py

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+"""
+Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
+
+An input string is valid if:
+
+Open brackets must be closed by the same type of brackets.
+Open brackets must be closed in the correct order.
+
+Question: https://leetcode.com/problems/valid-parentheses/
+
+
+"""
+
+
+class Solution:
+    def isValid(self, s: str) -> bool:
+        para = {')':'(', ']':'[', '}':'{'}
+        op = ['(','[', '{']
+        stack = []
+        
+        for c in s:
+            if c in op:
+                stack.append(c)
+            
+            elif c in para:
+                if len(stack) != 0 and stack[-1] == para[c]:
+                    stack.pop()
+                else:
+                    return False
+                    
+        if len(stack) == 0:
+            return True
+        else:
+            return False
+            
+            
+            
+            
+            
+            
+#             if c in para:
+#                 if len(stack) != 0 and stack[-1] == para[c]:
+#                     stack.pop()
+#                 else:
+#                     return False
+                
+#             else:
+#                 stack.append(c)
+                
+#         if len(stack) == 0:
+#             return True
+#         else:
+#             False

14. Questions/leetcode 21 - merge two sorted lists.py

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+"""
+You are given the heads of two sorted linked lists list1 and list2.
+
+Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.
+
+Return the head of the merged linked list.
+
+Question: https://leetcode.com/problems/merge-two-sorted-lists/
+
+"""
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+class Solution:
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        answer = ListNode()
+        tail = answer
+        while list1 and list2:
+            if list1.val < list2.val:
+                tail.next = list1
+                list1 = list1.next
+            else:
+                tail.next = list2
+                list2=list2.next
+            tail = tail.next
+            
+        if list1:
+                tail.next = list1
+        elif list2:
+                tail.next = list2
+                
+        return answer.next

14. Questions/leetcode 26 - remove duplicates from sorted array.py

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+"""
+Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same.
+
+Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the first part of the array nums. More formally, if there are k elements after removing the duplicates, then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements.
+
+Return k after placing the final result in the first k slots of nums.
+
+Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory.
+
+Question: https://leetcode.com/problems/remove-duplicates-from-sorted-array/
+
+"""
+
+class Solution:
+    def removeDuplicates(self, nums: List[int]) -> int:
+        list = 1
+        
+        for r in range(1, len(nums)):
+            if nums[r] != nums[r-1]:
+                nums[list] = nums[r]
+                list += 1
+                
+        return list

14. Questions/leetcode 27 - remove element.py

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+"""
+Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The relative order of the elements may be changed.
+
+Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the first part of the array nums. More formally, if there are k elements after removing the duplicates, then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements.
+
+Return k after placing the final result in the first k slots of nums.
+
+Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory.
+
+Question: https://leetcode.com/problems/remove-element/
+
+"""
+
+
+class Solution:
+    def removeDuplicates(self, nums: List[int]) -> int:
+        list = 1
+        
+        for r in range(1, len(nums)):
+            if nums[r] != nums[r-1]:
+                nums[list] = nums[r]
+                list += 1
+                
+        return list