642. Design Search Autocomplete System

Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character ‘#’).

You are given a string array sentences and an integer array times both of length n where sentences[i] is a previously typed sentence and times[i] is the corresponding number of times the sentence was typed. For each input character except ‘#’, return the top 3 historical hot sentences that have the same prefix as the part of the sentence already typed.

Here are the specific rules:

• The hot degree for a sentence is defined as the number of times a user typed the exactly same sentence before.
• The returned top 3 hot sentences should be sorted by hot degree (The first is the hottest one). If several sentences have the same hot degree, use ASCII-code order (smaller one appears first).
• If less than 3 hot sentences exist, return as many as you can.
• When the input is a special character, it means the sentence ends, and in this case, you need to return an empty list.

Implement the AutocompleteSystem class:

• AutocompleteSystem(String[] sentences, int[] times) Initializes the object with the sentences and times arrays.
• List input(char c) This indicates that the user typed the character c.

• Returns an empty array [] if c == ‘#’ and stores the inputted sentence in the system.
• Returns the top 3 historical hot sentences that have the same prefix as the part of the sentence already typed. If there are fewer than 3 matches, return them all.

305. Number of Islands II

You are given an empty 2D binary grid grid of size m x n. The grid represents a map where 0’s represent water and 1’s represent land. Initially, all the cells of grid are water cells (i.e., all the cells are 0’s).

We may perform an add land operation which turns the water at position into a land. You are given an array positions where positions[i] = [ri, ci] is the position (ri, ci) at which we should operate the ith operation.

Return an array of integers answer where answer[i] is the number of islands after turning the cell (ri, ci) into a land.

An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

774. Minimize Max Distance to Gas Station

You are given an integer array stations that represents the positions of the gas stations on the x-axis. You are also given an integer k.

You should add k new gas stations. You can add the stations anywhere on the x-axis, and not necessarily on an integer position.

Let penalty() be the maximum distance between adjacent gas stations after adding the k new stations.

Return the smallest possible value of penalty(). Answers within 10-6 of the actual answer will be accepted.

568. Maximum Vacation Days

LeetCode wants to give one of its best employees the option to travel among n cities to collect algorithm problems. But all work and no play makes Jack a dull boy, you could take vacations in some particular cities and weeks. Your job is to schedule the traveling to maximize the number of vacation days you could take, but there are certain rules and restrictions you need to follow.

Rules and restrictions:

1. You can only travel among n cities, represented by indexes from 0 to n - 1. Initially, you are in the city indexed 0 on Monday.
2. The cities are connected by flights. The flights are represented as an n x n matrix (not necessarily symmetrical), called flights representing the airline status from the city i to the city j. If there is no flight from the city i to the city j, flights[i][j] == 0; Otherwise, flights[i][j] == 1. Also, flights[i][i] == 0 for all i.
3. You totally have k weeks (each week has seven days) to travel. You can only take flights at most once per day and can only take flights on each week’s Monday morning. Since flight time is so short, we do not consider the impact of flight time.
4. For each city, you can only have restricted vacation days in different weeks, given an n x k matrix called days representing this relationship. For the value of days[i][j], it represents the maximum days you could take a vacation in the city i in the week j.
5. You could stay in a city beyond the number of vacation days, but you should work on the extra days, which will not be counted as vacation days.
6. If you fly from city A to city B and take the vacation on that day, the deduction towards vacation days will count towards the vacation days of city B in that week.
7. We do not consider the impact of flight hours on the calculation of vacation days.

Given the two matrices flights and days, return the maximum vacation days you could take during k weeks.

471. Encode String with Shortest Length

Given a string s, encode the string such that its encoded length is the shortest.

The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. k should be a positive integer.

If an encoding process does not make the string shorter, then do not encode it. If there are several solutions, return any of them.

1231. Divide Chocolate

You have one chocolate bar that consists of some chunks. Each chunk has its own sweetness given by the array sweetness.

You want to share the chocolate with your k friends so you start cutting the chocolate bar into k + 1 pieces using k cuts, each piece consists of some consecutive chunks.

Being generous, you will eat the piece with the minimum total sweetness and give the other pieces to your friends.

Find the maximum total sweetness of the piece you can get by cutting the chocolate bar optimally.

1100. Find K-Length Substrings With No Repeated Characters

Given a string s and an integer k, return the number of substrings in s of length k with no repeated characters.

733. Flood Fill

An image is represented by an m x n integer grid image where image[i][j] represents the pixel value of the image.

You are also given three integers sr, sc, and newColor. You should perform a flood fill on the image starting from the pixel image[sr][sc].

To perform a flood fill, consider the starting pixel, plus any pixels connected 4-directionally to the starting pixel of the same color as the starting pixel, plus any pixels connected 4-directionally to those pixels (also with the same color), and so on. Replace the color of all of the aforementioned pixels with newColor.

Return the modified image after performing the flood fill.

203. Remove Linked List Elements

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

21. Merge Two Sorted Lists

You are given the heads of two sorted linked lists list1 and list2.

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Return the head of the merged linked list.