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Posts tagged as “easy”

花花酱 LeetCode 1323. Maximum 69 Number

By zxi on January 20, 2020

Given a positive integer num consisting only of digits 6 and 9.

Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).

Example 1:

Input: num = 9669
Output: 9969
Explanation: 
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666. 
The maximum number is 9969.

Example 2:

Input: num = 9996
Output: 9999
Explanation: Changing the last digit 6 to 9 results in the maximum number.

Example 3:

Input: num = 9999
Output: 9999
Explanation: It is better not to apply any change.

Constraints:

  • 1 <= num <= 10^4
  • num‘s digits are 6 or 9.

Solution: Greedy

Replace the highest 6 to 9, if no 6, return the original number.

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

C++

花花酱 LeetCode 1317. Convert Integer to the Sum of Two No-Zero Integers

By zxi on January 13, 2020

Given an integer n. No-Zero integer is a positive integer which doesn’t contain any 0 in its decimal representation.

Return a list of two integers [A, B] where:

  • A and B are No-Zero integers.
  • A + B = n

It’s guarateed that there is at least one valid solution. If there are many valid solutions you can return any of them.

Example 1:

Example 2:

Example 3:

Example 4:

Example 5:

Constraints:

  • 2 <= n <= 10^4

Solution: Brute Force

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

C++

花花酱 LeetCode 1313. Decompress Run-Length Encoded List

By zxi on January 11, 2020

We are given a list nums of integers representing a list compressed with run-length encoding.

Consider each adjacent pair of elements [a, b] = [nums[2*i], nums[2*i+1]] (with i >= 0).  For each such pair, there are a elements with value b in the decompressed list.

Return the decompressed list.

Example 1:

Input: nums = [1,2,3,4]
Output: [2,4,4,4]

Constraints:

  • 2 <= nums.length <= 100
  • nums.length % 2 == 0
  • 1 <= nums[i] <= 100

Solution: Simulation

Time complexity: O(sum(n_i))
Space complexity: O(sum(n_i)) or O(1)

C++

花花酱 LeetCode 1304. Find N Unique Integers Sum up to Zero

By zxi on December 29, 2019

Given an integer n, return any array containing n unique integers such that they add up to 0.

Example 1:

Input: n = 5
Output: [-7,-1,1,3,4]
Explanation: These arrays also are accepted [-5,-1,1,2,3] , [-3,-1,2,-2,4].

Example 2:

Input: n = 3
Output: [-1,0,1]

Example 3:

Input: n = 1
Output: [0]

Constraints:

  • 1 <= n <= 1000

Solution: Generation

Use numbers from {-n/2, … n/2} + {0 if n is odd}

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

C++

花花酱 LeetCode 1299. Replace Elements with Greatest Element on Right Side

By zxi on December 28, 2019

Given an array arr, replace every element in that array with the greatest element among the elements to its right, and replace the last element with -1.

After doing so, return the array.

Example 1:

Input: arr = [17,18,5,4,6,1]
Output: [18,6,6,6,1,-1]

Constraints:

  • 1 <= arr.length <= 10^4
  • 1 <= arr[i] <= 10^5

Solution: Scan from right to left

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

C++