Leetcode

The problem in leetcode in java version

counter [since 3/31/2020]

• +5

leetcode number

• 36 Valid Sudoku [incomplete].
• 247 Strobogrammatic Number II [recursion(return each layer), time complexity?].
• 248 Strobogrammatic Number III [recursion(though dp may make faster), time?].
• 1186 Maximum Subarray Sum with One Deletion [O(n), dp(memory:O(1)), similar to maxium subarry]
• 53 Maximum Subarray [O(n), dp(memory:O(1))]
• 523 Continuous Subarray Sum [O(n^2), 1d dp(memory:O(n))]
  • Solution 1: sum[i, j] = dp[j] - dp[i]+arr[i] or
  • Solution 2: if a%k = c; b%k=c then(a-b)%k = 0(present it in hashmap)
• 1208 Get Equal Substrings Within Budget [understand problem and sliding window O(n)]
• 1209 Remove All Adjacent Duplicates in String II [stack unsolved and no edit yet....]
• 348 Design Tic-Tac-Toe [check continous n in board or using two rwos?? O(n*n) -> O(n)]
• 295 Find Median from Data Stream [two heaps(priority queue) O(lgn) to add number || balanced bst]
• 871 Minimum Number of Refueling Stops [heaps || ? o-1 kanpsack bags]
• 899 Orderly Queue [math and bubble sort || ? bfs tle]
• 1353 Maximum Number of Events That Can Be Attended [sort(by ending time) + greedy | bst+bs(?)]
• 1354 Construct Target Array With Multiple Sums [module, reverse or backtrack + maxheap]
• 3 Longest Substring Without Repeating Characters [two pointer + hashmap(while loop)]
• 159 Longest Substring with At Most Two Distinct Characters [two pointer + hashmap(for + while)]
• 340 Longest Substring with At Most K Distinct Characters [same as 159]
• 395 Longest Substring with At Least K Repeating Characters [divide and conquer(time?) | 2nd solution?]
• 953 Verifying an Alien Dictionary [logic and corner case | pre for Alein dictionary]
• 53 maximum subarray [greedy [O(n)] | divide and conquer ? how and time]
• 122 Best Time to Buy and Sell Stock II [greedy + math(what is the minimal profit:MaxNum-MinNum)]
• 678 Valid Parenthesis String [low and high two pointer to indicate the min and max left open bracket][or using recursion]
• 468 Validate IP Address [regex | mix with regex, if else, for]
• 829 Consecutive Numbers Sum [math problem (kx = ), | citadel OA 2020 ]
• 606 Construct String from Binary Tree [build a tree with recursion and stack]
• 205 Isomorphic Strings [map each character | convert string to number | Isomorphic] (7/12/2021)
• 408 Valid Word Abbreviation [recursion | two pointers ?] (7/18/2021)
• 605 Can Place Flowers [check and set | easy]
• 674 Longest Continuous Increasing Subsequence [two pointers]
• 670 Maximum Swap [hashmap: O(n^2)-> O(n)]
• 983 Minimum Cost For Tickets [dp | dp[i] = dp[i+7] or dp[i+30] or dp[i+1] | dp[i] = dp[i-1] dp[i-7]]
• 1522 Diameter of N-Ary Tree [recursion | great problem to practice height and depth recursively]

To do list

• 755 Pour Water [related to trapping rain water]
• alein dictionary [Topological sort: find cycle in graph | dfs backtrack?]
• 289 game of life [in place array]
• summary in [3,159,340,395]
• divide and conquer [53]
• 1163 Last Substring in Lexicographical Order: really make me upset
• 1396 Design Underground System 【10/8/2020】

Amaazon interview

• trapping rain water
• 159 Longest Substring with At Most Two Distinct Characters (my interview 3/19) (round 1)
• swap nodes in pairs (my interview 3/20) (round 4)
• next challenges related to this problem[1249. Minimum Remove to Make Valid Parentheses]

Citadel

• Intern OA (3/7/2021)
  • Triplets: 259. 3Sum Smaller (long need to convert sum to long or using a + b < sum -c)
  • inversions: [5,4,3,2,1] cout how many inversion subsequence such than a[i]>a[j]>a[k] when i < j < k;
    • using merge sort [https://leetcode.com/discuss/interview-question/661336/google-onsite-count-increasing-subsequences/646088]
    • same as countTriplets

Problem Collections

• 单调栈
• jump game collections [array greedy
• 连续数组之和 prefix sum (a%K+K)%K [523、525、560、974] [724, 713]

Tron inteerview

Onsite

• 200 number of island (Feb 2020)

Always remember: no md, no accepted

• when you do not want write the md, that equals you solve nothing.
• However you are familiar with the problem, time will make you weak.