Hard

LeetCode 3651 note: compute layer by layer over teleports; arriving at a cell by teleport costs the previous layer’s minimum over cells with value >= it, found with a running minimum after sorting, followed by the usual right / down grid DP

LeetCode 312 note: choose the last balloon k burst in the range (i, j); at that moment its neighbors are i and j, and the two sides are independent subproblems

LeetCode 2603 note: trim coin-free leaves, trim exactly two more layers, and walk each remaining edge twice

LeetCode note for Minimum Swaps To Make Sequences Increasing, rebuilt from the original learning note

LeetCode note for Best Time to Buy and Sell Stock IV, rebuilt from the original learning note

LeetCode note for Best Time to Buy and Sell Stock III, rebuilt from the original learning note

LeetCode 759 note: k-way merge all work intervals by start; any gap after the latest end so far is common free time

LeetCode 3910 note: n is tiny, so enumerate subsets with a bitmask, check the even sum first, then check that the induced subgraph is connected

LeetCode note for Alien Dictionary, rebuilt from the original learning note

LeetCode 3906 note: the range reaches 9 × 10^15, so no per-number checks; a digit DP carries both lower and upper tight flags, plus the previous digit on the path since path cells must be non-decreasing

LeetCode note for Swim in Rising Water, rebuilt from the original learning note

LeetCode note for Sort Items by Groups Respecting Dependencies, rebuilt from the original learning note