Find the number I in the sorted array

Topic describes

Count the number of occurrences of a number in a sorted array.Copy the code

The sample

Example 1: input nums = [5,7,7,8,8,10], target = 8 output: 2 example 2: input nums = [5,7,7,8,8,10], target = 6 output: 0Copy the code

The problem solving

from collections import Counter

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        for k, v in dict(Counter(nums)).items():
            if k == target:
                return v
        return 0
Copy the code

Count the number of occurrences of elements, so again, Counter.

Turn Counter(nums) statistics into dict and iterate over the keys and values in the dict. When key==target, print value.

Powers of two, two

Topic describes

Given an integer n, determine whether the integer is a power of 2. If so, return true; Otherwise, return false. If there is an integer x such that n == 2x, n is considered to be a power of 2.Copy the code

The sample

Example 1: Input: n = 1 Output: true Description: 20 = 1 Example 2: Input: n = 16 Output: true Description: 24 = 16 Example 3: Input: n = 3 Output: false Example 4: Input: n = 4 Output: true Example 5: Input: n = 5 Output: false Warning: -2^31 <= n <= 2^ 31-1Copy the code

The problem solving

class Solution:
    BIG = 2**30
    def isPowerOfTwo(self, n: int) -> bool:
        return n > 0 and Solution.BIG % n == 0
Copy the code

A number n is a power of 2 if and only if n is a positive integer. -2^31 <= n <= 2^31-1 = 2^31-1 = n <= 2^31-1 = n <= 2^31-1 = 2^30

Valid letter heterotopic words

Topic describes

Given two strings s and t, write a function to determine whether t is an alphabetic allotopic of S.Copy the code

The sample

Example 1: Enter s = "anagram", t = "nagaram" Output: true Example 2: Enter S = "rat", t = "car" Output: falseCopy the code

The problem solving

from collections import Counter

class Solution:
    def isAnagram(self, s: str, t: str) -> bool:
        return dict(Counter(s)) == dict(Counter(t))
Copy the code

If two strings have the same number of occurrences of each character, then they are valid alphabetic anagrams.

You can use Counter to count the frequency of occurrences of characters in each input parameter, convert it into a dict, and then determine if the two dictionaries are equal.

Merge two ordered arrays

Topic describes

Merge nums2 into nums1 to make nums1 an ordered array. Initialize nums1 and nums2 to m and n, respectively. You can assume that nums1 has a space size equal to m + n so that it has enough space to hold elements from Nums2.Copy the code

The sample

Example 1: Input nums1 = [1,2,3,0,0], m = 3, nums2 = [2,5,6], n = 3 Output: [1,2,2,3,5,6] Nums1 = [1], m = 1, nums2 = [], n = 0Copy the code

The problem solving

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        nums1[m:] = nums2
        return nums1.sort()
Copy the code

Just concatenate and sort.

Notice that there are two requirements for the length of the list, m and n. So nums1 concatenates nums2 from the MTH, then sort using sort().

5. Adjust the array order so that the odd number precedes the even number

Topic describes

Take an array of integers and implement a function to adjust the order of the numbers in the array so that all odd numbers are in the first half of the array and all even numbers are in the second half.Copy the code

The sample

Example: input: nums = [1,2,3,4] output: [1,3,2,4] note: [3,1,2,4] is also one of the correct answers.Copy the code

The problem solving

class Solution:
    def exchange(self, nums: List[int]) -> List[int]:
        list_odd = []
        list_even = []
        for i in nums:
            if i % 2 == 0:
                list_even.append(i)
            else:
                list_odd.append(i)
        return list_odd + list_even
Copy the code

In the easiest way to understand. Iterate through the input list, then judge the elements and add them to the corresponding two arrays.

Finally, add the even number list_even to the odd number list_odd.