LC 206, 21, 23, 88, 127, 139, 204, 232, 346, 496, 503
206. Reverse Linked List
- Reverse the pointer to point the previous element, both in iteration and recursion
- Linkedlist
21. Merge Two Sorted Lists
- Just like merge sort, both in iteration and recursion
- Merge sort, Linkedlist
23. Merge k Sorted Lists
- Use priority queue
88. Merge Sorted Array
- Merge from the end and just like merge sort
- Array, Merge sort
127. Word Ladder
- The BFS queue stores all the possible strings; remember to delete from the set or use visited array to mark the visited strings
- BFS
139. Word Break
- Only when the substring(j, i) is in wordDict and dp[j] = true, set dp[i] = true
- dp
204. Count Primes
- Mark all the possible product i * j as true
- Math, DP
232. Implement Queue using Stacks
- Pop twice to make sure the sequence is the same
- stack, queue
346. Moving Average from Data Stream
- Use queue to store the number, use a variable to track the sum
- Queue
496. Next Greater Element I
- Use a stack to record the element in descending order
- Stack
503. Next Greater Element II
- Tranverse the array twice, but the second time not push in the stack
- Stack
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