Sliding Window: 121. Buy and Sell Stock | 3. Longest Substring | Contains Duplicate II

121. Best Time to Buy and Sell Stock

Easy

You are given an array prices where prices[i] is the price of a given stock on the ith day.

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

 

Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.

Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.

Solution:

class Solution:

def maxProfit(self, prices: List[int]) -> int:

l,r=0,1 #left , right pointer

maxP=0

while r < len(prices):

if prices[l]< prices[r]:

profit = prices[r]-prices[l]

maxP = max(maxP, profit)

if prices[l]> prices[r]:

l = r

r+=1

return maxP

3. Longest Substring Without Repeating Characters

Medium

Given a string s, find the length of the longest  without duplicate characters.

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3. Note that "bca" and "cab" are also correct answers.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Solution:

class Solution:

def lengthOfLongestSubstring(self, s: str) -> int:

l =0 # left , right pointer

a = set()

res =0

# enumerate gives us the index 'r' AND the character 'c'

for r,c in enumerate(s):

while c in a: # in s=pwwtfg remove form left(l) till c value is removed from set a.

a.remove(s[l])

l+=1

a.add(c)

res= max(res, r-l+1)

return res

219. Contains Duplicate II

Easy

Given an integer array nums and an integer k, return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k.

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false

Constraints:

• 1 <= nums.length <= 105
• -109 <= nums[i] <= 109
• 0 <= k <= 105

class Solution:

def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:

w=set()

l=0

for r, c in enumerate(nums):

if r-l > k:

w.remove(nums[l])

l+=1

if c in w:

return True

w.add(c)

return False

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