Environment: Python 3.8

Key technique: if

Given a string s consisting of only the characters 'a' and 'b', return true if every 'a' appears before every 'b' in the string. Otherwise, return false.

Example 1:

Input: s = "aaabbb"
Output: true
Explanation:
The 'a's are at indices 0, 1, and 2, while the 'b's are at indices 3, 4, and 5.
Hence, every 'a' appears before every 'b' and we return true.

Analysis:

1. check pattern “ba” is matched with s.
2. If yes, return False. Else, return True.

Solution:

class Solution:
    def checkString(self, s):
        if "ba" in s:
            return False
        else:
            return True

Submissions:

Environment: Python 3.8

Key technique: str(), int()

Reversing an integer means to reverse all its digits.

• For example, reversing 2021 gives 1202. Reversing 12300 gives 321 as the leading zeros are not retained.

Given an integer num, reverse num to get reversed1, then reverse reversed1 to get reversed2. Return true if reversed2 equals num. Otherwise return false.

Example 1:

Input: num = 526
Output: true
Explanation: Reverse num to get 625, then reverse 625 to get 526, which equals num.

Analysis:

1. Convert input to string format and reverse it
2. Convert it to int format.
3. Convert it to a string format and reverse it.
4. If input equal converted result, return pass.
5. Else, return Fail.

Solution:

class Solution:
    def isSameAfterReversals(self, num):
        temp=str(num)
        temp=int(temp[::-1])
        temp=str(temp)
        temp=temp[::-1]
        if int(temp) ==num:
            return True
        else:
            return False

Submissions:

Environment: Python 3.8

Key technique: split

A sentence is a list of words that are separated by a single space with no leading or trailing spaces.

You are given an array of strings sentences, where each sentences[i] represents a single sentence.

Return the maximum number of words that appear in…

Environment: Python 3.8

Key technique: Counter, |, max

Two strings word1 and word2 are considered almost equivalent if the differences between the frequencies of each letter from 'a' to 'z' between word1 and word2 is at most 3.

Given two strings word1 and word2, each of length n, return true…

Environment: Python 3.8

Key technique: for, [::-1]

Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string "".

A string is palindromic if it reads the same forward and backward.

Example 1:

Input: words = ["abc","car","ada","racecar","cool"]
Output: "ada"
Explanation: The first string that is palindromic is "ada".
Note that "racecar" is also palindromic, but it is not the first.

Analysis:

1. Reverse input string
2. If string == reversed string, return it.
3. If no string and reversed string is equal, return ‘’

Solution:

class Solution:
    def firstPalindrome(self, words):
        for i in words:
            if i==i[::-1]:
                return i
        return ''

Submissions:

Reference:

https://leetcode.com/problems/find-first-palindromic-string-in-the-array/discuss/1639462/Python-99-faster-Simple-Solution

Environment: Python 3.8

Key technique: split, isdecimal, for, if, append

A sentence is a list of tokens separated by a single space with no leading or trailing spaces. …

Environment: Python 3.8

Key technique: set, if, for

There are n rings and each ring is either red, green, or blue. The rings are distributed across ten rods labeled from 0 to 9.

You are given a string rings of length 2n that describes the n rings that are placed…

Environment: Python 3.8

Key technique: enumerate, if

There are n houses evenly lined up on the street, and each house is beautifully painted. You are given a 0-indexed integer array colors of length n, where colors[i] represents the color of the ith house.

Return the maximum distance between two houses…