档案日期2015的23

题目描述：

Invert a binary tree.

     4
   /   \
  2     7
 / \    / \
1   3   6  9

to

     4
   /   \
  7     2
 / \   / \
9   6  3  1

Trivia:

This problem was inspired by this original ...

题目描述：

Implement the following operations of a stack using queues.

push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
empty() -- Return whether the stack is ...

题目描述：

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .

You may assume that the ...

题目描述：

Find the total area covered by two rectilinear rectangles in a 2D plane.

Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.

Assume that the total area is never beyond ...