Problem description:

On an NxN chessboard, a knight starts at the r-th row and c-th column and attempts to make exactly K moves. The rows and columns are 0 indexed, so the top-left square is (0, 0), and the bottom-right square is (N-1, N-1).

Problem description:

Solution:

time complexity: $O()$
space complexity: $O()$
reference:

Problem description:

In this problem, a rooted tree is a directed graph such that, there is exactly one node (the root) for which all other nodes are descendants of this node, plus every node has exactly one parent, except for the root node which has no parents.

Problem description:

Solution:

time complexity: $O()$
space complexity: $O()$
reference:

Problem description:

In 2D space, m people, n bikes, with the following conditions

Problem description:

log timestamp. implement start(id, timestamp), end(id, timestamp), print the log in ascending time order.

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Union find is frequently used in graph problem. Pretty useful in cycle detection.

Problem description:

We have a grid of 1s and 0s; the 1s in a cell represent bricks. A brick will not drop if and only if it is directly connected to the top of the grid, or at least one of its (4-way) adjacent bricks will not drop.

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For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees.

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In a string composed of ‘L’, ‘R’, and ‘X’ characters, like “RXXLRXRXL”, a move consists of either replacing one occurrence of “XL” with “LX”, or replacing one occurrence of “RX” with “XR”. Given the starting string start and the ending string end, return True if and only if there exists a sequence of moves to transform one string to the other.