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Posts tagged as “easy”

花花酱 LeetCode 2032. Two Out of Three

Given three integer arrays nums1nums2, and nums3, return distinct array containing all the values that are present in at least two out of the three arrays. You may return the values in any order.

Example 1:

Input: nums1 = [1,1,3,2], nums2 = [2,3], nums3 = [3]
Output: [3,2]
Explanation: The values that are present in at least two arrays are:
- 3, in all three arrays.
- 2, in nums1 and nums2.

Example 2:

Input: nums1 = [3,1], nums2 = [2,3], nums3 = [1,2]
Output: [2,3,1]
Explanation: The values that are present in at least two arrays are:
- 2, in nums2 and nums3.
- 3, in nums1 and nums2.
- 1, in nums1 and nums3.

Example 3:

Input: nums1 = [1,2,2], nums2 = [4,3,3], nums3 = [5]
Output: []
Explanation: No value is present in at least two arrays.

Constraints:

  • 1 <= nums1.length, nums2.length, nums3.length <= 100
  • 1 <= nums1[i], nums2[j], nums3[k] <= 100

Solution: Hashmap / Bitmask

s[x] := bitmask of x in all array[i]

s[x] = 101 => x in array0 and array2

Time complexity: O(n1 + n2 + n3)
Space complexity: O(n1 + n2 + n3)

C++

花花酱 LeetCode 2037. Minimum Number of Moves to Seat Everyone

There are n seats and n students in a room. You are given an array seats of length n, where seats[i] is the position of the ith seat. You are also given the array students of length n, where students[j] is the position of the jth student.

You may perform the following move any number of times:

  • Increase or decrease the position of the ith student by 1 (i.e., moving the ith student from position x to x + 1 or x - 1)

Return the minimum number of moves required to move each student to a seat such that no two students are in the same seat.

Note that there may be multiple seats or students in the same position at the beginning.

Example 1:

Input: seats = [3,1,5], students = [2,7,4]
Output: 4
Explanation: The students are moved as follows:
- The first student is moved from from position 2 to position 1 using 1 move.
- The second student is moved from from position 7 to position 5 using 2 moves.
- The third student is moved from from position 4 to position 3 using 1 move.
In total, 1 + 2 + 1 = 4 moves were used.

Example 2:

Input: seats = [4,1,5,9], students = [1,3,2,6]
Output: 7
Explanation: The students are moved as follows:
- The first student is not moved.
- The second student is moved from from position 3 to position 4 using 1 move.
- The third student is moved from from position 2 to position 5 using 3 moves.
- The fourth student is moved from from position 6 to position 9 using 3 moves.
In total, 0 + 1 + 3 + 3 = 7 moves were used.

Example 3:

Input: seats = [2,2,6,6], students = [1,3,2,6]
Output: 4
Explanation: The students are moved as follows:
- The first student is moved from from position 1 to position 2 using 1 move.
- The second student is moved from from position 3 to position 6 using 3 moves.
- The third student is not moved.
- The fourth student is not moved.
In total, 1 + 3 + 0 + 0 = 4 moves were used.

Constraints:

  • n == seats.length == students.length
  • 1 <= n <= 100
  • 1 <= seats[i], students[j] <= 100

Solution: Greedy

Sort both arrays, move students[i] to seats[i].

Time complexity: O(nlogn)
Space complexity: O(1)

C++

花花酱 LeetCode 2042. Check if Numbers Are Ascending in a Sentence

A sentence is a list of tokens separated by a single space with no leading or trailing spaces. Every token is either a positive number consisting of digits 0-9 with no leading zeros, or a word consisting of lowercase English letters.

  • For example, "a puppy has 2 eyes 4 legs" is a sentence with seven tokens: "2" and "4" are numbers and the other tokens such as "puppy" are words.

Given a string s representing a sentence, you need to check if all the numbers in s are strictly increasing from left to right (i.e., other than the last number, each number is strictly smaller than the number on its right in s).

Return true if so, or false otherwise.

Example 1:

example-1
Input: s = "1 box has 3 blue 4 red 6 green and 12 yellow marbles"
Output: true
Explanation: The numbers in s are: 1, 3, 4, 6, 12.
They are strictly increasing from left to right: 1 < 3 < 4 < 6 < 12.

Example 2:

Input: s = "hello world 5 x 5"
Output: false
Explanation: The numbers in s are: 5, 5. They are not strictly increasing.

Example 3:

example-3
Input: s = "sunset is at 7 51 pm overnight lows will be in the low 50 and 60 s"
Output: false
Explanation: The numbers in s are: 7, 51, 50, 60. They are not strictly increasing.

Example 4:

Input: s = "4 5 11 26"
Output: true
Explanation: The numbers in s are: 4, 5, 11, 26.
They are strictly increasing from left to right: 4 < 5 < 11 < 26.

Constraints:

  • 3 <= s.length <= 200
  • s consists of lowercase English letters, spaces, and digits from 0 to 9, inclusive.
  • The number of tokens in s is between 2 and 100, inclusive.
  • The tokens in s are separated by a single space.
  • There are at least two numbers in s.
  • Each number in s is a positive number less than 100, with no leading zeros.
  • s contains no leading or trailing spaces.

Solution: String

Time complexity: O(n)
Space complexity: O(1)

C++

花花酱 LeetCode 2027. Minimum Moves to Convert String

You are given a string s consisting of n characters which are either 'X' or 'O'.

move is defined as selecting three consecutive characters of s and converting them to 'O'. Note that if a move is applied to the character 'O', it will stay the same.

Return the minimum number of moves required so that all the characters of s are converted to 'O'.

Example 1:

Input: s = "XXX"
Output: 1
Explanation: XXX -> OOO
We select all the 3 characters and convert them in one move.

Example 2:

Input: s = "XXOX"
Output: 2
Explanation: XXOX -> OOOX -> OOOO
We select the first 3 characters in the first move, and convert them to 'O'.
Then we select the last 3 characters and convert them so that the final string contains all 'O's.

Example 3:

Input: s = "OOOO"
Output: 0
Explanation: There are no 'X's in s to convert.

Constraints:

  • 3 <= s.length <= 1000
  • s[i] is either 'X' or 'O'.

Solution: Straight Forward

if s[i] == ‘X’, change s[i], s[i + 1] and s[i + 2] to ‘O’.

Time complexity: O(n)
Space complexity: O(1)

C++

花花酱 LeetCode 1903. Largest Odd Number in String

You are given a string num, representing a large integer. Return the largest-valued odd integer (as a string) that is a non-empty substring of num, or an empty string "" if no odd integer exists.

substring is a contiguous sequence of characters within a string.

Example 1:

Input: num = "52"
Output: "5"
Explanation: The only non-empty substrings are "5", "2", and "52". "5" is the only odd number.

Example 2:

Input: num = "4206"
Output: ""
Explanation: There are no odd numbers in "4206".

Example 3:

Input: num = "35427"
Output: "35427"
Explanation: "35427" is already an odd number.

Constraints:

  • 1 <= num.length <= 105
  • num only consists of digits and does not contain any leading zeros.

Solution: Find right most odd digit

We just need to find the right most digit that is odd, answer will be num[0:r].

Answer must start with num[0].
Proof:
Assume the largest number is num[i:r] i > 0, we can always extend to the left, e.g. num[i-1:r] which is also an odd number and it’s larger than num[i:r] which contradicts our assumption. Thus the largest odd number (if exists) must start with num[0].

Time complexity: O(n)
Space complexity: O(1)

C++