Graph

LeetCode 1377 note: undirected edges, seen must hold nodes, and an early arrival depends on whether the frog can still move

LeetCode 2392 note: row and column conditions are independent, so run one topological sort for each; put x at its row and column positions, and return an empty matrix if either has a cycle

LeetCode 2421 note: add nodes in increasing value order and count same-value nodes per Union-Find group

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

LeetCode note for Network Delay Time, rebuilt from the original learning note

LeetCode 1059 note: trim outdegrees backward from the destination; a node is safe only when every outgoing edge leads to a safe node, and the destination itself must have no outgoing edges

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 note for Cheapest Flights Within K Stops, rebuilt from the original learning note

LeetCode note for Path With Minimum Effort, rebuilt from the original learning note

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

LeetCode 1514 note: multiplying probabilities only shrinks them, so Dijkstra applies; prune with <=