jackiephy / leetcode_array

leetcode_array

Starting today, I will use github to record my leetcode brushing experience. I will put the questions, answers and thoughts of each day in github for reference. The first part is named 'leetcode_array', I will pick out some questions related to array for practice.

I will put these questions into this repository:

1. Remove Element
2. Remove Duplicates from Sorted Array
3. Remove Duplicates from Sorted Array II
4. Find the Celebrity  Locked
5. Rotate Array
6. First Missing Positive
7. Bulls and Cows
8. Gas Station
9. Pascal's Triangle
10. Pascal's Triangle II
11. Majority Element
12. Majority Element II
13. H-Index
14. H-Index II Binary Search
15. Shortest Word Distance
16. Shortest Word Distance II
17. Shortest Word Distance III
18. Contains Duplicate
19. Contains Duplicate II
20. Contains Duplicate III
21. Jump Game
22. Jump Game II
23. Best Time to Buy and Sell Stock
24. Best Time to Buy and Sell Stock II
25. Best Time to Buy and Sell Stock III
26. Best Time to Buy and Sell Stock IV
27. Best Time to Buy and Sell Stock with Cooldown
28. Container With Most Water
29. Trapping Rain Water
30. Increasing Triplet Subsequence
31. Longest Consecutive Sequence
32. Maximum Gap Bucket
33. Find the Duplicate Number
34. Candy
35. Patching Array
36. Median of Two Sorted Arrays
37. Create Maximum Number
38. Count of Range Sum
39. Game of Life
40. Insert Interval
41. Merge Intervals
42. Meeting Rooms
43. Meeting Rooms II
44. Data Stream as Disjoint Intervals TreeMap
45. Sliding Window Maximum
46. Find Median from Data Stream
47. Maximum Subarray
48. Maximum Size Subarray Sum Equals k
49. Minimum Size Subarray Sum
50. Product of Array Except Self
51. Maximum Product Subarray
52. Summary Ranges
53. Missing Ranges
54. Merge Sorted Array
55. Sort Colors
56. Move Zeroes
57. Wiggle Subsequence
58. Wiggle Sort
59. Wiggle Sort II

2019/4/8 completed list:

27. Remove Element  easy

• Given an array nums and a value val, remove all instances of that value in-place and return the new length. Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory. The order of elements can be changed. It doesn't matter what you leave beyond the new length.

• Example 1: Given nums = [3,2,2,3], val = 3, Your function should return length = 2, with the first two elements of nums being 2. It doesn't matter what you leave beyond the returned length.

• Example 2: Given nums = [0,1,2,2,3,0,4,2], val = 2, Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4. Note that the order of those five elements can be arbitrary. It doesn't matter what values are set beyond the returned length.

26. Remove Duplicates from Sorted Array  easy

• Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

• Example 1: Given nums = [1,1,2], Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn't matter what you leave beyond the returned length.

• Example 2: Given nums = [0,0,1,1,1,2,2,3,3,4], Your function should return length = 5, with the first five elements of nums being modified to 0, 1, 2, 3, and 4 respectively. It doesn't matter what values are set beyond the returned length.

80. Remove Duplicates from Sorted Array II  medium

• Given a sorted array nums, remove the duplicates in-place such that duplicates appeared at most twice and return the new length. Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

• Example 1: Given nums = [1,1,1,2,2,3], Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3 respectively. It doesn't matter what you leave beyond the returned length.

• Example 2: Given nums = [0,0,1,1,1,1,2,3,3], Your function should return length = 7, with the first seven elements of nums being modified to 0, 0, 1, 1, 2, 3 and 3 respectively. It doesn't matter what values are set beyond the returned length.

2019/4/9 completed list:

189. Rotate Array  easy

• Given an array, rotate the array to the right by k steps, where k is non-negative.

• Example 1:
  Input: [1,2,3,4,5,6,7] and k = 3
  Output: [5,6,7,1,2,3,4]
  Explanation:
  rotate 1 steps to the right: [7,1,2,3,4,5,6]
  rotate 2 steps to the right: [6,7,1,2,3,4,5]
  rotate 3 steps to the right: [5,6,7,1,2,3,4]

• Example 2:
  Input: [-1,-100,3,99] and k = 2
  Output: [3,99,-1,-100]
  Explanation:
  rotate 1 steps to the right: [99,-1,-100,3]
  rotate 2 steps to the right: [3,99,-1,-100]

41. First Missing Positive  hard

• Given an unsorted integer array, find the smallest missing positive integer.

• Example 1:
  Input: [1,2,0]
  Output: 3

• Example 2:
  Input: [3,4,-1,1]
  Output: 2

• Example 3:
  Input: [7,8,9,11,12]
  Output: 1

299. Bulls and Cows  medium

• You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your friend makes a guess, you provide a hint that indicates how many digits in said guess match your secret number exactly in both digit and position (called "bulls") and how many digits match the secret number but locate in the wrong position (called "cows"). Your friend will use successive guesses and hints to eventually derive the secret number.
  Write a function to return a hint according to the secret number and friend's guess, use A to indicate the bulls and B to indicate the cows.
  Please note that both secret number and friend's guess may contain duplicate digits.

• Example 1:
  Input: secret = "1807", guess = "7810"
  Output: "1A3B"
  Explanation: 1 bull and 3 cows. The bull is 8, the cows are 0, 1 and 7.

• Example 2:
  Input: secret = "1123", guess = "0111"
  Output: "1A1B"
  Explanation: The 1st 1 in friend's guess is a bull, the 2nd or 3rd 1 is a cow.

2019/4/11 completed list:

134. Gas Station  medium

• There are N gas stations along a circular route, where the amount of gas at station i is gas[i].
  You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an empty tank at one of the gas stations.
  Return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1.

• Example 1:
  Input:
  gas = [1,2,3,4,5]
  cost = [3,4,5,1,2]
  Output: 3
  Explanation:
  Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4
  Travel to station 4. Your tank = 4 - 1 + 5 = 8
  Travel to station 0. Your tank = 8 - 2 + 1 = 7
  Travel to station 1. Your tank = 7 - 3 + 2 = 6
  Travel to station 2. Your tank = 6 - 4 + 3 = 5
  Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3.
  Therefore, return 3 as the starting index.

• Example 2:
  Input:
  gas = [2,3,4]
  cost = [3,4,3]
  Output: -1
  Explanation:
  You can't start at station 0 or 1, as there is not enough gas to travel to the next station.
  Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4
  Travel to station 0. Your tank = 4 - 3 + 2 = 3
  Travel to station 1. Your tank = 3 - 3 + 3 = 3
  You cannot travel back to station 2, as it requires 4 unit of gas but you only have 3.
  Therefore, you can't travel around the circuit once no matter where you start.