Leetcode-75-Study-Plan

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Level 1

Day 1 - Prefix Sum

Running Sum of 1d Array (easy)

• Time Complexity: O(n)
• Space Complexity: O(1)

class Solution:
    def runningSum(self, nums: List[int]) -> List[int]:
        prefix = 0
        for i in range(len(nums)):
            prefix += nums[i]
            nums[i] = prefix
        return nums

Find Pivot Index (easy)

• Time Complexity: O(n)
• Space Complexity: O(1)

class Solution:
    def pivotIndex(self, nums: List[int]) -> int:
        leftSum = 0
        totalSum = sum(nums)

        for i in range(len(nums)):
            if totalSum - nums[i] == leftSum:
                return i
            else:
                totalSum -= nums[i]
                leftSum += nums[i]

        return -1

Day 2 - String

Isomorphic Strings (easy)

• Time Complexity: O(n)
• Space Complexity: O(n)

class Solution:
    def isIsomorphic(self, s: str, t: str) -> bool:
        keys = list({a:b for a,b in zip(s,t)}.keys())
        values = list({a:b for a,b in zip(t,s)}.values())
        return keys == values

Is Subsequence (easy)

• Time Complexity: O(n)
• Space Complexity: O(1)

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        if len(s) > len(t):
            return False
        if not s:
            return True

        s_ptr = 0
        for char in t:
            if s_ptr <= len(s)-1:
                if s[s_ptr] == char:
                    s_ptr += 1

        return len(s) == s_ptr

Day 3 - Linked List

• Merge Two Sorted Lists (easy)
• Reverse Linked List (easy)

Day 4 - Linked List

• Middle of the Linked List (easy)
• Linked List Cycle II (medium)

Day 5 - Greedy

• Best Time to Buy and Sell Stock (easy)
• Longest Palindrome (easy)

Day 6 - Tree

• N-ary Tree Preorder Traversal (easy)
• Binary Tree Level Order Traversal (medium)

Day 7 - Binary Search

• Binary Search (easy)
• First Bad Version (easy)

Day 8 - Binary Search Tree

• Validate Binary Search Tree (medium)
• Lowest Common Ancestor of a Binary Search Tree (medium)

Day 9 - Graph/BFS/DFS

• Flood Fill (medium)
• Number of Islands (medium)

Day 10 -Dynamic Programming

• Fibonacci Number (easy)
• Climbing Stairs (easy)

Day 11 -Dynamic Programming

• Min Cost Climbing Stairs (easy)
• Unique Paths (medium)

Day 12 -Sliding Window/Two Pointer

• Find All Anagrams in a String (medium)
• Longest Repeating Character Replacement (medium)

Day 13 -Hashmap

• Two Sum (easy)
• Bulls and Cows (medium)

Day 14 -Stack

• Backspace String Compare (easy)
• Decode String (medium)

Day 15 -Heap

• Last Stone Weight (easy)
• Top K Frequent Words (medium)

Level 2

Level 3