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Given the `root` of a binary tree, check whether it is a mirror of itself (i.

of elements in `nums1` and `nums2` respectively.

Given an `m x n` grid of characters `board` and a string `word`, return `true` if word exists in the grid.

included in the window.

Given an integer array `nums` of **unique** elements, return all possible subsets (the power set).

Given an array of integers `heights` representing the histogram's bar height where the width of each bar is `1`, return the area of the largest rectangle in the histogram.

order red, white, and blue.

我昔东海上，劳山餐紫霞。

You are climbing a staircase.