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Handout #2  Homework # 1 CS4040/5040

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Handout #2
Homework # 1
CS4040/5040 (100/110 pts)
1. (60 pts.) Analyzing Code. For each of the following, answer parts a-e.
a.) (5pts.) Is the code correct? If not, provide a counterexample.
b.) (3pts.) What is the asymptotic worst-case time complexity of the code.
c.) (2pts.) What is the asymptotic worst-case space complexity of the code.
d.) (3pts.) What is the asymptotic best-case time complexity of the code.
e.) (2pts.) What is the asymptotic best-case space complexity of the code.
i.) (15pts.) Maximum element (note this code is not the same as in the example in
Notes3)
double Max(double a[], int b, int e)
{
if (b>=e) {
return a[b];
} else {
int m=(b+e)/2;
return(fmax(Max(a, b, m), Max(a, m+1, e)));
}
}
// The following is the top level call to Max.
// Returns the largest element in a. There are n elements in a[]
double Max(double a[], int n)
{
return(Max(a, 0, n-1));
}
ii.) (15pts.) Sequential Search version 1
%% Determines if element x is in array a, by looking at the
%% first 1/3, then the middle 1/3, finally at the last 1/3.
%%
int Find(double x, double a[], int b, int e) {
int n=e-b+1;
switch (n) {
case 0:
case 1:
return((a[e]==x)?e+1:0);
case 2:
return((a[b]==x)?(b+1):((a[e]==x)?(e+1):0));
}
int m1=b+n/3;
int m2=b+(2*n)/3;
int res1=Find(x, a, b, m1);
if (res1==0) {
int res2=Find(x, a, m1+1, m2);
if (res2==0) {
int res3=Find(x, a, m2+1, e);
if (res3==0) {
return(0);
} else return(res3);
} else return(res2);
} else return(res1);
}
// The following is the top level call to Find.
1
Handout #2 September 1, 2021
// Returns 0 if x is not in a, or index between 1 and n if it is.
// There are n elements in a.
int Find(double x, double a[], int n) {
return(Find(x, a, 0, n-1));
}
iii.) (15pts.) Sequential Search version 2
int Find2(double x, double a[], int b, int e)
{
if (b>=e){
return(0);
}
if (a[b]==x) {
return(b+1);
} else {
return(Find2(x,a,b+1,e));
}
}
// The following is the top level call to Find2.
// Returns 0 if x is not in a, or index between 1 and n if it is.
// There are n elements in a.
int Find2(double x, double a[], int n)
{
return(Find2(x, a, 0, n-1));
}
iv.) (15pts.) Do two arrays hold the same elements (possibly in a different order.)
// Returns true if the two arrays hold the exact same
// elements (not necessarily in the same order).
//
// We may assume that the two arrays are of the same size,
// otherwise they cannot possibly hold the same elements.
bool EqualSets(int a[], int b[], int n)
{
for (int i=0;i<n;++i){
bool found=false;
for (int j=0;j<n;++j) {
if (a[i]==b[j]) {
found = true;
break;
}
}
if (!found) {
return(false);
}
}
return(true);
}
2. (30 pts.) Prove or disprove by using the definition that:
(a) (10 pts.) 2n ∈ O(6n
2 + n + 42)
(b) (10 pts.) 2n
2 ∈ o(3n
2 + 12n)
(c) (10 pts.) 3n
2 + 42 ∈ Ω(4n + 1)
3. (10 pts.) Answer true or false to each of the following. You do not have to provide
justification.
(a) 10 + n + n
2 ∈ O(n
2
)
2
Handout #2 September 1, 2021
(b) 10 + n + n
2 ∈ Θ(n
2
)
(c) 10 + n + n
2 ∈ Ω(n)
(d) 10 + n + n
2 ∈ Θ(n)
(e) 10 + n + log n ∈ Ω(n)
(f) 10 + n + log n ∈ O(n
2
)
(g) 7 log2 n + 2n log n ∈ O(n)
(h) 7 log2 n + 2n log n ∈ Ω(log n)
(i)
1
3
n
+ 100 ∈ O(1)
(j) 3n + 100 ∈ O(1)
CS5040 students must also do the following problem
4. (10 pts.) Exercise 2-4, page 41

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