归档 2015年6月

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 tweet by Max Howell:

Google: 90% of our engineers use the software ...

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 empty.

Notes:
You ...

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 given expression is always valid ...

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 ...

题目描述：

Given a complete binary tree, count the number of nodes.

Definition of a complete binary tree from Wikipedia:

In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level ...