2267. Check if There Is a Valid Parentheses String Path
A parentheses string is a non-empty string consisting only of ‘(‘ and ‘)’. It is valid if any of the following conditions is true:
- It is ().
- It can be written as AB (A concatenated with B), where A and B are valid parentheses strings.
- It can be written as (A), where A is a valid parentheses string.
You are given an m x n matrix of parentheses grid. A valid parentheses string path in the grid is a path satisfying all of the following conditions:
- The path starts from the upper left cell (0, 0).
- The path ends at the bottom-right cell (m - 1, n - 1).
- The path only ever moves down or right.
- The resulting parentheses string formed by the path is valid.
Return true if there exists a valid parentheses string path in the grid. Otherwise, return false.
Alice is texting Bob using her phone. The mapping of digits to letters is shown in the figure below.
In order to add a letter, Alice has to press the key of the corresponding digit i times, where i is the position of the letter in the key.
- For example, to add the letter ‘s’, Alice has to press ‘7’ four times. Similarly, to add the letter ‘k’, Alice has to press ‘5’ twice.
- Note that the digits ‘0’ and ‘1’ do not map to any letters, so Alice does not use them.
However, due to an error in transmission, Bob did not receive Alice’s text message but received a string of pressed keys instead.
- For example, when Alice sent the message “bob”, Bob received the string “2266622”.
Given a string pressedKeys representing the string received by Bob, return the total number of possible text messages Alice could have sent.
Since the answer may be very large, return it modulo 109 + 7.
2263. Make Array Non-decreasing or Non-increasing
You are given a 0-indexed integer array nums. In one operation, you can:
- Choose an index i in the range 0 <= i < nums.length
- Set nums[i] to nums[i] + 1 or nums[i] - 1
Return the minimum number of operations to make nums non-decreasing or non-increasing.
1508. Range Sum of Sorted Subarray Sums
You are given the array nums consisting of n positive integers. You computed the sum of all non-empty continuous subarrays from the array and then sorted them in non-decreasing order, creating a new array of n * (n + 1) / 2 numbers.
Return the sum of the numbers from index left to index right (indexed from 1), inclusive, in the new array. Since the answer can be a huge number return it modulo 109 + 7.
225. Implement Stack using Queues
Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).
Implement the MyStack class:
- void push(int x) Pushes element x to the top of the stack.
- int pop() Removes the element on the top of the stack and returns it.
- int top() Returns the element on the top of the stack.
- boolean empty() Returns true if the stack is empty, false otherwise.
Notes:
- You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
- Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.