CMSI 386: Programming Languages: Homework #2

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1. Write a JavaScript function that accepts a number of U.S. cents and returns an array containing,
respectively, the smallest number of U.S. quarters, dimes, nickels, and pennies that equal the given amount.
> change(96)
[3, 2, 0, 1]
> change(8)
[0, 0, 1, 3]
2. Write a JavaScript function that takes in a string s and returns the string which is equivalent to s but with all
ASCII vowels removed.
> stripVowels(“Hello, world”)
‘Hll, wrld’
3. Write a JavaScript function that randomly permutes a string. By random we mean that each time you call the
function for a given argument all possible permutations are equally likely (note that “random” is not the same
as “arbitrary”).
> scramble(“Hello, world”)
‘w,dlroH elol’
4. Write a JavaScript function that yields successive powers of two starting at 1 and going up to some limit.
Consume the values with a callback.
> powersOfTwo(70, function (p) {console.log(p);})
1
2
4
8
16
32
64
5. Write a JavaScript function that yields powers of an arbitrary base starting at exponent 0 and going up to
some limit. Consume the values with a callback.
> powers(3, 400, function (p) {console.log(p);})
1
3
9
27
81
243
6. Write a JavaScript function that interleaves two arrays. If the arrays do not have the same length, the
elements of the longer array should end up at the end of the result array.
> interleave([“a”, “b”], [1, 2, true, null])
[“a”, 1, “b”, 2, true, null]
7. Write a JavaScript function that doubles up each item in a list.
> stutter([5,4,[3],9])
[5,5,4,4,[3],[3],9,9]
8. Write a JavaScript function that produces a word count object from a string. Consider the words of the string
to be any sequence of one or more Latin letters plus the apostrophe. (Yes, that means you can “throw away”
all non-Latin letters, because, well, ES5 JavaScript doesn’t have \p{L} in its regexes. Argh.) Your script
should treat the words case-insensitively, so just lowercase everything.
> wordCount(“If you dog a dog, you’ll\nbe DOG-TIRED.”)
{“if”:1, “you”:1, “dog”:3, “a”:1, “you’ll”:1, “be”:1, “tired”:1}
9. Flesh out the unit tests for problems 1-8 that I have started here for you.
$(function(){
varanagram=function(s,t){
if(s.length!==t.length){
returnfalse;
}
vara=s.split(“”),b=t.split(“”);
return$(a).not(b).length===0&&$(b).not(a).length===0
};
test(“ChangeTests”,function(){
deepEqual(change(97),[3,2,0,2]);
deepEqual(change(8),[0,0,1,3]);
//Moreneeded
});
test(“StripVowelsTests”,function(){
deepEqual(stripVowels(“Hello,world”),”Hll,wrld”);
//Moreneeded
});
test(“ScrambleTests”,function(){
vardata=[“”,”a”,”rat”,”zzz”,”^*&^*&^ªÄÈËɡɳɷ”]
data.forEach(function(s){
ok(anagram(s,scramble(s)));
});
});
test(“PowersofTwoTests”,function(){
//Implementthese
1/30/2014 CMSI 386: Programming Languages: Homework #2
http://cs.lmu.edu/~ray/classes/pl/assignment/2/ 3/3
});
//Testpowershere
//Testinterleavehere
//Teststutterhere
//Testwordcounthere
});
Use the following HTML driver for the tests:
javascriptwarmup.html




JavaScriptWarmupTest







10. Write a JavaScript script that writes successive prefixes of the value entered into a web page text field into
new div elements, one after another, starting with the first prefix, which is zero characters long. The new
divs should be added approximately one second apart.
Assuming the string “matsumoto” were entered, the divs would be:
m
ma
mat
mats
matsu
matsum
matsumo
matsumot
matsumoto