# Pengfei Liu

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**Content Feed**

Solved

How long is the longest prime diagonal?

Stanislaw Ulam once observed that if the counting numbers are <http://en.wikipedia.org/wiki/Ulam_spiral arranged in a spiral>, t...

4 months ago

Solved

Spot the outlier

All points except for one lie on a line. Which one is the outlier? Example: You are given a list of x-y pairs in a column ...

4 months ago

Solved

Find the biggest empty box

You are given a matrix that contains only ones and zeros. Think of the ones as columns in an otherwise empty floor plan. You wan...

5 months ago

Solved

Mechanics 1

I thought I would make a mechanics problem for all those physics lovers out there. Imagine two solid, rigid spheres B1 and B...

5 months ago

Solved

Determine if input is odd

Given the input n, return true if n is odd or false if n is even.

5 months ago

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Pangrams!

A pangram, or holoalphabetic sentence, is a sentence using every letter of the alphabet at least once. Example: Input s ...

5 months ago

Solved

Counting Money

Add the numbers given in the cell array of strings. The strings represent amounts of money using this notation: $99,999.99. E...

5 months ago

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Nearest Numbers

Given a row vector of numbers, find the indices of the two nearest numbers. Examples: [index1 index2] = nearestNumbers([2 5 3...

5 months ago

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Sort a list of complex numbers based on far they are from the origin.

Given a list of complex numbers z, return a list zSorted such that the numbers that are farthest from the origin (0+0i) appear f...

5 months ago

Solved

Remove all the words that end with "ain"

Given the string s1, return the string s2 with the target characters removed. For example, given s1 = 'the main event' your ...

5 months ago

Solved

Most nonzero elements in row

Given the matrix a, return the index r of the row with the most nonzero elements. Assume there will always be exactly one row th...

5 months ago

Solved

Create times-tables

At one time or another, we all had to memorize boring times tables. 5 times 5 is 25. 5 times 6 is 30. 12 times 12 is way more th...

5 months ago

Solved

Binary numbers

Given a positive, scalar integer n, create a (2^n)-by-n double-precision matrix containing the binary numbers from 0 through 2^n...

5 months ago

Solved

Quote Doubler

Given a string s1, find all occurrences of the single quote character and replace them with two occurrences of the single quote ...

5 months ago

Solved

Pascal's Triangle

Given an integer n >= 0, generate the length n+1 row vector representing the n-th row of <http://en.wikipedia.org/wiki/Pascals_t...

5 months ago

Solved

Return a list sorted by number of occurrences

Given a vector x, return a vector y of the unique values in x sorted by the number of occurrences in x. Ties are resolved by a ...

5 months ago

Solved

Which values occur exactly three times?

Return a list of all values (sorted smallest to largest) that appear exactly three times in the input vector x. So if x = [1 2...

5 months ago

Solved

Reverse Run-Length Encoder

Given a "counting sequence" vector x, construct the original sequence y. A counting sequence is formed by "counting" the entrie...

5 months ago

Solved

Cell joiner

You are given a cell array of strings and a string delimiter. You need to produce one string which is composed of each string fr...

5 months ago

Solved

Find the alphabetic word product

If the input string s is a word like 'hello', then the output word product p is a number based on the correspondence a=1, b=2, ....

5 months ago

Solved

Subset Sum

Given a vector v of integers and an integer n, return the the indices of v (as a row vector in ascending order) that sum to n. I...

5 months ago

Solved

Trimming Spaces

Given a string, remove all leading and trailing spaces (where space is defined as ASCII 32). Input a = ' singular value deco...

5 months ago

Solved

Make a Palindrome Number

Some numbers like 323 are palindromes. Other numbers like 124 are not. But look what happens when we add that number to a revers...

5 months ago

Solved

Which doors are open?

There are n doors in an alley. Initially they are all shut. You have been tasked to go down the alley n times, and open/shut the...

5 months ago

Solved

Extract leading non-zero digit

<http://en.wikipedia.org/wiki/Benford%27s_law Benford's Law> states that the distribution of leading digits is not random. This...

5 months ago

Solved

Making change

Given an amount of currency, return a vector of this form: [100 50 20 10 5 2 1 0.5 0.25 0.1 0.05 0.01] Example: Input a = ...

5 months ago

Solved

Sums with Excluded Digits

Add all the integers from 1 to n in which the digit m does not appear. m will always be a single digit integer from 0 to 9. no...

5 months ago

Solved

Times 2 - START HERE

Try out this test problem first. Given the variable x as your input, multiply it by two and put the result in y. Examples:...

5 months ago

Solved

Make the vector [1 2 3 4 5 6 7 8 9 10]

In MATLAB, you create a vector by enclosing the elements in square brackets like so: x = [1 2 3 4] Commas are optional, s...

5 months ago

Solved

Find the sum of all the numbers of the input vector

Find the sum of all the numbers of the input vector x. Examples: Input x = [1 2 3 5] Output y is 11 Input x ...

5 months ago