�ݺ�ߣ

Programming
Exercises
Terry Yin

Question
Does software company need to
train programmers?

7

ProjectEuler.net
"Project Euler exists to encourage, challenge, and develop the skills and enjoyment of anyone with
an interest in the fascinating world of mathematics."

? Project Euler is a series of challenging mathematical/computer

programming problems that requires more than just mathematical
insights to solve.

10

Expectations

Mathematics
lution implementing
So
rfor mance co d ing
Hig h pe
So lving problem
ind ivi dually

13

Example: Quick & Dirty
Once you solved a problem, you are entitled to join the forum for this problem.You can
share your solution with the other people who have also solved it. And the post usually
start with this sentence:!

Good coding habit?

14

int i, j, k, n, sum;!
int factorial[10000];!

"

? It��s too simple for

?
?

Java, Ruby or Python,
for which they can
handle big numbers by
default."
So let��s look at C/C++."
Real code copied from
the forum.

int* getfactorial(int n)!
{!
factorial[0] = 1;!
k = 0;!
for(i = 2; i <= n; i++)!
{!
for(j = 0; j <= k; j++)!
factorial[j] *= i;!
for(j = 0; j <= k; j++)!
{!
if(factorial[j] >= 10)!
{!
factorial[j+1] += (factorial[j] - (factorial[j] % 10)) / 10;!
factorial[j] = factorial[j] % 10;!
if(j == k)!
k++;!
}!
}!
}!
return factorial;!
}!

"

int getsum(int* array, int k)!
{!
sum = 0;!
for(i = 0; i <= k; i++)!
sum += array[i];!
return sum;!
}!

"

int main()!
{!
int* factorial = getfactorial(n);!
sum = getsum(factorial, k);!
cout << "nThe sum of the digits of " << n << "! is " << sum << ".n";!
return 0;!
16
}!

Big number again. Ha ha, I did that
before! Let me reuse it...

18

#include<iostream>!

"

using namespace std;!

"

int i, j, k, n, sum;!
int factorial[10000];!

"

Why the big number is named ��factorial��
in my previous implementation?

int* getfactorial(int n)!
{!
factorial[0] = 1;!
k = 0;!
for(i = 2; i <= n; i++)!
{!
for(j = 0; j <= k; j++)!
factorial[j] *= i;!
for(j = 0; j <= k; j++)!
{!
if(factorial[j] >= 10)!
{!
factorial[j+1] += (factorial[j] - (factorial[j] % 10)) / 10;!
factorial[j] = factorial[j] % 10;!
if(j == k)!
k++;!
}!
}!
}!
return factorial;!
}

Where��s the code for big number?

19

#include <stdio.h>

"

#define NUMB 120
#define SIZE 1000000000

"
OK, too hard to reuse. It��s not
that hard to invent the wheel again.

// 9 * 120 = 1080 total digits.
// 9 digit numbers

int main() {
int i = 0;
int j = 0;
int bigNum1[NUMB];
int bigNum2[NUMB];
int bigNum3[NUMB];
int counter = 0;

"

"
"

"
}

for (i = 0;
bigNum1 =
bigNum2 =
bigNum3 =
}

i < NUMB; i++) {
0;
0;
0;

bigNum1[0] = 1;
bigNum2[0] = 1;
counter = 2;
i = 0;
while (i == 0) {
counter++;
for (j = 0; j < NUMB; j++) {
bigNum3[j] = bigNum2[j] + bigNum1[j];
}
for (j = 0; j < NUMB-1; j++) {
while (bigNum3[j] >= SIZE) {
bigNum3[j] -= SIZE;
bigNum3[j+1]++;
}
}
if (bigNum3[111] >= 1)
break;
for (j = 0; j < NUMB; j++) {
bigNum1[j] = bigNum2[j];
bigNum2[j] = bigNum3[j];
}
}
printf("n");
printf("P025 answer = %u", counter);

20

s
ng exercise
i
oblem so lv
Pr
tant skills
ver y impor
? Train
inter view
s
ten use d a
Of

?

ques tions
n skills in
i
ly also tra
? Probab
able co de,
n
ng maintai
maki
a little.

?Don��t do it before bed time...

21

Functional Test

Integration Test

Unit Test
27

Code Retreat
A day-long practice-intensive event for programmers, !
popularized by Corey Haines.

?
?
?
?
?
?
?
32

Poker Hands in ProjectEuler
? This is not a very hard problem to solve,
?

comparing to most of the problems listed in
ProjectEuler.net"
But it��s hard to solve it without bugs if you don��t
have unit tests."

? Problem 54 in projectEuler.net

36

Example: Complicated
Transaction

37

Why Did I Do It Right
With Only One Try?

38

TEST(poker_hand, comparing){
CHECK(pokerHand("4H 5C 6S 7S TD")< pokerHand("2C 3S 7S 8D KD"));
CHECK(!(pokerHand("4H 5C 6S 7S KD")< pokerHand("2C 3S 7S 8D TD")));
CHECK(pokerHand("4H 5C 6S 7S KD")> pokerHand("2C 3S 7S 8D TD"));
}
TEST(poker_hand, compare_cards){
CHECK(pokerHand("3H 5C 6S 7S 8D")< pokerHand("4H 5C 6S 7S 9D"));
CHECK(pokerHand("3H 5C 6S 7S 9D")< pokerHand("4H 5C 6S 7S TD"));
CHECK(pokerHand("3H 5C 6S 7S TD")< pokerHand("4H 5C 6S 7S JD"));
CHECK(pokerHand("3H 5C 6S 7S JD")< pokerHand("4H 5C 6S 7S QD"));
CHECK(pokerHand("3H 5C 6S 7S QD")< pokerHand("4H 5C 6S 7S KD"));
CHECK(pokerHand("3H 5C 6S 7S KD")< pokerHand("4H 5C 6S 7S AD"));
}
TEST(poker_hand, compare_high_cards_2nd){
}
TEST(poker_hand, compare_high_cards_3nd_4th_5th){
}
TEST(poker_hand, compare_high_card_and_one_pair){
}
TEST(poker_hand, compare_one_pairs){
CHECK(pokerHand("3H 5C 6S 9S 9D")> pokerHand("3H 5C 7S 8S 8D"));
CHECK(pokerHand("5C 6S 9S 9D KD")> pokerHand("5C 7S 8S 8D AD"));
CHECK(pokerHand("5C 6S 9S 9D KD")< pokerHand("5C 7S 9S 9D AD"));
}

"

...
39

Do deliberate exercises.
Alone and with the others.
Always use good practices.
Have fun.

40

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