Leetcode 143. Reorder List. Python

143. Reorder List

You are given the head of a singly linked-list. The list can be represented as:

L0 → L1 → … → Ln - 1 → Ln

Reorder the list to be on the following form:

L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …

You may not modify the values in the list's nodes. Only nodes themselves may be changed.

Solution :

class Solution:
    def reorderList(self, head: Optional[ListNode]) -> None:
        
        # searching middle
        s, f = head, head.next
        while f and f.next:
            s = s.next
            f = f.next.next
            
        # second half reversing
        sec = s.next
        prev = s.next = None
        while sec:
            temp = sec.next
            sec.next = prev
            prev = sec
            sec = temp
            
        # merging both
        fir, sec = head, prev
        while sec :
            t1, t2 = fir.next, sec.next
            fir.next = sec
            sec.next = t1
            fir, sec = t1, t2

Explaination :

Comments

Leetcode 371. Sum of Two Integers. C++ / Java

371 . Sum of Two Integers Given two integers a and b , return the sum of the two integers without using the operators + and - . Example 1: Input: a = 1, b = 2 Output: 3 Example 2: Input: a = 2, b = 3 Output: 5 Constraints: -1000 <= a, b <= 1000 Solution : C++ : class Solution { public: int getSum(int a, int b) { if (b==0) return a; int sum = a ^ b; int cr = (unsigned int) (a & b) << 1; return getSum(sum, cr); } }; Java : class Solution { public int getSum(int a, int b) { while(b != 0){ int tmp = (a & b) << 1; a = a ^ b; b = tmp; } return a; } } Explaination :

Container with Most Water - Leetcode 11 - Python

You are given an integer array height of length n . There are n vertical lines drawn such that the two endpoints of the i th line are (i, 0) and (i, height[i]) . Find two lines that together with the x-axis form a container, such that the container contains the most water. Return the maximum amount of water a container can store . Notice that you may not slant the container. Input: height = [1,8,6,2,5,4,8,3,7] Output: 49 Explanation: The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49. class Solution: def maxArea(self, height: List[int]) -> int: # ans = 0 # for l in range(len(height)): # for r in range(l+1, len(height)): # ...

Leetcode 424. Longest Repeating Character Replacement. Python (Sliding Window)

424 . Longest Repeating Character Replacement You are given a string s and an integer k . You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations . Example 1: Input: s = "ABAB", k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = "AABABBA", k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA". The substring "BBBB" has the longest repeating letters, which is 4. Constraints: 1 <= s.length <= 10 5 s consists of only uppercase English letters. 0 <= k <= s.length Solution : class Solution: def characterReplacement(self, s: str, k: int) -> int: hm = {} ans = 0 ...

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