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Introduction to Data Structures ������
2019 Spring Semester
Joonwon Lee
College of Software
2
Instructor informationn Joonwon Lee
n Professor in College of Softwaren Research areas
n Computer Systems
n Contact informationn [email protected] http://csl.skku.edu/People/Joonn Corporate Collaboration Center #85572n Office hour: by appointment
3
Course information
n Class hours
n Tuesday 12:00 – 13:15
n Thursday 13:30 – 14:45
n Language: English
n Classroom: 23217
n Prerequisite: C programming languagen You SHOULD know how to program using C (e.g., pointer)
n If you don’t know how to use pointer, please drop this course!
n Course website
n http://www.icampus.ac.kr
4
What is this course?
n In computer science, a data structure is a data organization, management and storage format that enables efficient access and modification. More precisely, a data structure is a collection of data values, the relationships among them, and the functions or operations that can be applied to the data. [Wikipedia]
n Class goalsn Learn data structure, which is a way of collecting and organizing data in a
computer to perform operations on the data efficientlyn Cover arrays, stacks, queues, linked lists, tree, graph, hashing, search and
sorting algorithms
5
Lecture notesn Textbook
n Fundamentals of data structures in C by Horowits, Sanhni and Anderson-Freed (2nd, 2008)
n Lecture Notesn Adapt Prof. Jinkyu Lee’s slidesn which is also from Prof. Jongwuk Lee’s slides.
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Gradingn Attendance: 10%
n You will be given F if you are absent eight times or more.n Alternative attendance approval: to follow SKKU rule
n Assignments: 30%n Six programming homeworksn Academic honesty is truly needed since the penalty is severe
n Mid-term exam: 30%
n Final exam: 30%
7
Gradingn If you have any plan to be absent with reasonable reasons, please tell
me in advance!
n Cheating will lead you to fail this course with “F” grade.
n You will be given F if you are absent eight times or more.
n The 50% A and 90% guideline is merely an upper-limit by SKKU.
8
Tentative schedule and topics
Week 1: Course introduction, C overview
Week 2: Performance analysis, recursion Homework 1
Week 3: Stacks
Week 4: Stacks Homework 2
Week 5: Queues
Week 6: Lists Homework 3
Week 7: Trees
Week 8: Mid-term examApril 22nd Tuesday 12:00-15:00
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Tentative schedule and topics
Week 9: Mid-term review, Trees 10/29: Homework 4 out
Week 10: Graphs
Week 11: Graphs 11/12: Homework 5 out
Week 12: Sorting
Week 13: Sorting 11/26: Homework 6 out
Week 14:Hashing
Week 15: Reserved
Week 16: Final exam June 18th Tuesday 12:00 – 15:00
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TAn To be updated
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Do we have to use only English?n You are recommended to use English only.
n Assignmentn Your program (C code): only in English n Your report: either in English or Korean
n Examn All questions: written in Englishn Your answers: either in English or Korean
n Outside of the classn Questions through email: either in English or Korean
n In-classn ?
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Any question?n And, any suggestion?
Basics of data structures
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Definitionn Definition of data structure
n An organization of information, usually in memory, for better algorithm efficiency
n Queue, stack, linked list, heap, dictionary, tree, etc.
n Definition of algorithmn What is an algorithm?n What is an efficient algorithm?
n An algorithm which spends less resources: time and space
15
Definitionn Definition of an algorithm: a finite set of instructions that should
satisfy
1) Input: zero or more inputs
2) Output: at least one output
3) Definiteness: clear and unambiguous instructions
4) Finiteness: terminating after a finite number of steps
5) Effectiveness (Machine-executable): basic enough to be carried out
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Programn Program
Program = Data Structure + Algorithm
How to store data in computer memory
How to handle the stored data
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Examplen Example 1
n Question 1: sort 100 records.n Question 2: sort 1,000,000 records.
Question 1 Question 2
Insertion Sort c1*104 unit time c1*1012 unit time
Heap sort c2*102 unit time c2*106 unit time
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Examplen Example 2
n Question 1: You have a lot data. You frequently search for some data.n Question 2: You have the same data. You frequently insert and delete some
data.
Question 1 Question 2
Array c11* log n unit time c12* n unit time
Linked-List c21* n unit time c22 unit time
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Overviewn What to learn in Data Structure
n Some theory and data structure to efficiently store and manipulate datan Some algorithms and examples
n Examplen Data structure: array, list, queue, tree, graph, sorting, hashing, heap, etc.n Algorithm: sorting, searching, minimum spanning tree, shortest path
algorithm, etc.n Theory: abstract data types, performance analysis
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Overviewn Data Structure course vs. Algorithm course
Program = Data Structure + Algorithm
Data Structure + Algorithm
Data Structure Course
Data Structure + Algorithm
Algorithm Course
Review on C Programming
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Review on C Programmingn What should you do with the C programming?
n How to use an array and a pointern Understand the relationship between the array and the pointer.n Use dynamic memory allocation.
n How to define a structure and make use of itn Understand self-referential structures.
n How to use recursive programmingn Transform iterative programming into recursive programming.
n To take this course, I strongly recommend that you have taken Cprogramming!
23
What is Array?n Definition
n A collection of elements with same data typesn Each element is sequential in memory.
n Array indexn Each element can be referenced by an index.n Index ranges: [0] ~ [size – 1]
int score[10];
Data type Array name Array size
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Example: Arrayn Input five numbers and print them reversely.
#include <stdio.h>
#define ARRAY_SIZE 5
int main()
{
int numbers[ARRAY_SIZE], i;
printf("Input five numbers\n");
for (i = 0; i < ARRAY_SIZE; i++)
scanf("%d", &numbers[i]);
for (i = ARRAY_SIZE - 1; i >= 0; i--)
printf("%d ", numbers[i]);
return 0;
}
25
Function Call with Arrayn Calculating the average of values in array
#include <stdio.h>#define ARRAY_SIZE 5
void inputNumbers(int num[], int len);double computeAverage(int num[], int len);
int main(){
int numbers[ARRAY_SIZE];
inputNumbers(numbers, ARRAY_SIZE);printf("average: %.3lf", computeAverage(numbers, ARRAY_SIZE));
return 0;}
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Function Call with Arrayn Calculating the average of values in array
void inputNumbers(int num[], int len){
int i;for (i = 0; i < len; i++)
scanf("%d", &num[i]);}
double computeAverage(int num[], int len){
int total = 0, i;for (i = 0; i < len; i++)
total = total + num[i];return total / (double)len;
}
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Two-Dimensional Arrayn Filling all entries in the two-dimensional matrix
int row, col, matrix[6][6];
for (row = 0; row < 6; row++) {
for (col = 0; col < 6; col++){
if (row < col)matrix[row][col] = 1;
else if (row == col)matrix[row][col] = 0;
elsematrix[row][col] = -1;
}}
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int scores[10]; int matrix[6][6];
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What is Pointer?n Definition
n A variable to store a memory address instead of a value
3
00FDFC18
n
Value
AddressName
00FDFC18
0070FA44
pn
int n = 3;
int* pn = &n;
Variable
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& (Ampersand) Operatorn Reference operator
n Return the address of an variable.
65 (‘A’) c
00FDFC18
pc00FDFC1C
00FDFC19
00FDFC1A
00FDFC1B
00FDFC1C
00FDFC1D
00FDFC1E
00FDFC1F
char* pc
65 (‘A’)
cpc
#include <stdio.h>
int main()
{
char c = 'A';
char* pc = &c;
printf("%c %p\n", c, pc);
printf("%p %p\n", &c, &pc);
printf("%d %d\n", sizeof(c), sizeof(pc));
return 0;
}
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& (Ampersand) Operatorn What is the size of a pointer variable?
n
00FDFC18
pn00FDFC1C00FDFC19
00FDFC1A
00FDFC1B
00FDFC1C
00FDFC1D
00FDFC1E
00FDFC1F
int* pn
3
npn
3
#include <stdio.h>
int main(){int n = 3;int* pn = &n;
printf("%d %p\n", n, pn);printf("%p %p\n", &n, &pn);printf("%d %d\n", sizeof(n), sizeof(pn));
return 0;}
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* (Asterisk) Operatorn Dereference operator
n Return the value at the pointer address.
67 (‘C’) c
00FDFC18
pc00FDFC1C00FDFC19
00FDFC1A
00FDFC1B
00FDFC1C
00FDFC1D
00FDFC1E
00FDFC1F
char* pc#include <stdio.h>
int main(){
char c = 'A';char* pc = &c;
printf("%c %c\n", c, *pc);
*pc = 'C';printf("%c %c\n", c, *pc);
return 0;}
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Example: Pointern Use address and dereference operators correctly.
#include <stdio.h>
int main(){
int a, b, c;int *p, *q, *r;
a = 6, b = 10;p = &b, q = p, r = &c;p = &a, *q = 8, *r = *p;*r = a + *q + *&c;
printf("%d %d %d", a, b, c);
return 0;}
34
Example: Pointer
#include <stdio.h>
int main(){
int a, b, c;int *pa = &a, *pb = &b, *pc = &c;
*pa = 10, *pb = 20;*pc = *pa + *pb;
printf("%d %d %d", a, b, c);
return 0;}
35
Functional Call with Pointern Two types for inter-function communication
n Call by value: passing by valuen Call by reference: passing by address
#include <stdio.h>
void swap1(int x, int y);void swap2(int* px, int* py);
int main(){
int a = 5, b = 7;swap1(a, b);printf("%d %d\n", a, b);swap2(a, b);printf("%d %d\n", a, b);return 0;
}
void swap1(int x, int y){
int temp = x;x = y;y = temp;
}
void swap2(int* px, int* py){
int temp = *px;*px = *py;*py = temp;
}
36
Pointer to Pointern We can use a pointer that points to another pointer.
#include <stdio.h>
int main(){char c = 'A';char* pc = &c;char** ppc = &pc;
printf("%p %p\n", pc, ppc);printf("%d %d\n", sizeof(pc), sizeof(ppc));
return 0;} 65 (‘A’) c
pc0062Fd90
ppc00FDFD84
char **ppc
&pc
&c
&ppc 0062FD78
0062FD79
0062FD7A
0062FD7B
00FDFD84
00FDFD85
00FDFD86
00FDFD87
0062Fd90
0062Fd91
37
Arithmetic Operation for Pointern How does the char pointer work?
#include <stdio.h>
int main(){char c = 'A';char* pc = &c;char** ppc = &pc;
printf("%p %p\n", pc, ppc);printf("%p %p\n", pc + 1, ppc + 1);printf("%p %p\n", &c, &c + 1);printf("%p %p\n", &pc, &ppc);printf("%p %p\n", &pc + 1, &ppc + 1);
return 0;}
65 (‘A’) c
0062Fd90
00FDFD84
char **ppc
&pc
&c
&ppc 0062FD78
0062FD79
0062FD7A
0062FD7B
00FDFD84
00FDFD85
00FDFD86
00FDFD87
0062Fd90
0062Fd91
38
Arithmetic Operation for Pointern How does the int pointer work?
#include <stdio.h>
int main(){int n = 10;int* pn = &n;int** ppn = &pn;
printf("%p %p\n", pn, ppn);printf("%p %p\n", pn + 1, ppn + 1);printf("%p %p\n", &n, &n + 1);printf("%p %p\n", &pn, &ppn);printf("%p %p\n", &pn + 1, &ppn + 1);
return 0;}
n
pn0062Fd90
20
ppn00FDFD84
int** ppn
&pn
&ppn
+1
&n
0062FD78
0062FD79
0062FD7A
0062FD7B
00FDFD84
00FDFD85
00FDFD86
00FDFD87
0062Fd90
0062Fd91
0062Fd92
0062Fd93
39
Array and Pointern The pointer to the first element of the array can be used as the name of
the array.
#include <stdio.h>
int main(){int a[6] = { 5, 3, 1, 2, 4, 6 };int* pa = a;
printf("%d %d\n", *a, *pa);printf("%p %p\n", a, pa);printf("%p %p\n", &a, &pa);
printf("%d %d\n", a[0], pa[0]);printf("%d %d\n", a[1], pa[1]);return 0;
}
int a[6];
5312
00FDFC18
00FDFC1C
00FDFC20
00FDFC24
a[0]
a[1]
a[2]
a[3]
4Bytea
00FDFC28
6a[4]
a[5]00FDFC2C
4
00FDFC30
*(a + 0)
*(a + 1)
*(a + 2)
*(a + 3)
*(a + 4)
*(a + 5)
00FDFC18 pa00FDFC3C
40
Example: Array and Pointern Is it a correct code?
1234
65
a pi
pend-1440986684
00FDFC18
00FDFC1C
00FDFC20
00FDFC24
00FDFC28
00FDFC2C00FDFC30
#include <stdio.h>
int main(){
int a[6] = { 1, 2, 3, 4, 5, 6 };int *pend = a + 6;int *pi = NULL;
for (pi = a; pi < pend; pi++)printf("%d\n", *pi);
return 0;}
41
Example: Array and Pointern Print the smallest array value using pointers.
#include <stdio.h>int main(){
int a[6] = { 32, 12, 31, 42, 15, 24 };int *pend = a + 6;int *psmallest = a;int *pi = NULL;
for (pi = a; pi < pend; pi++){
if (*pi < *psmallest)psmallest = pi;
}printf("%d", *psmallest);return 0;
}
32123142
2415
a psmallest
pend-1440986684
00FDFC18
00FDFC1C
00FDFC20
00FDFC24
00FDFC28
00FDFC2C00FDFC30
42
Passing Array to Functionn Passing a pointer (instead of an array) to a function
#include <stdio.h>void printArray(int* pa, int len);
int main(){
int a[5] = { 5, 3, 2, 1, 4 };printArray(a, 5);return 0;
}
void printArray(int* pa, int len){
int i;for (i = 0; i < len; i++)
printf("%d\n", pa[i]);}
int a[5];
5321
00FDFC18
00FDFC1C
00FDFC20
00FDFC24
a[0]
a[1]
a[2]
a[3]
4Bytea
00FDFC28 a[4]00FDFC2C
4
00FDFC3000FDFC18 pa
43
Example: Passing Array to Functionn Multiplying 4 for each element in an array
#include <stdio.h>void multiply4(int* pa, int len);
int main(){int a[5] = { 5, 3, 2, 1, 4 }, i;multiply4(a, 5);for (i = 0; i < 5; i++)printf("%d\n", a[i]);
return 0;}void multiply4(int* pa, int len){int i;for (i = 0; i < len; i++)pa[i] = pa[i] * 4;
}
int a[5];
5321
00FDFC18
00FDFC1C
00FDFC20
00FDFC24
a[0]
a[1]
a[2]
a[3]
4Bytea
00FDFC28 a[4]
00FDFC2C
4
00FDFC3000FDFC18 pa
44
How to Use Memory in Cn Conceptual view of memory used in C program
45
Dynamic Memory Allocation
#include <stdio.h>#include <stdlib.h>
int main(){
int size, i;scanf("%d", &size);// Allocate dynamic memoryint* pn = malloc(sizeof(int)* size);for (i = 0; i < size; i++)
scanf("%d", &pn[i]);
for (i = 0; i < size; i++)printf("%d\n", pn[i]);
free(pn); // Release memory
return 0;}
46
Dynamic Memory Allocationn Is it a correct code?
#include <stdio.h>#include <stdlib.h>
int *genNumbers(int size);
int main(){
int size, i;scanf("%d", &size);
int *pn = genNumbers(size);for (i = 0; i < size; i++)
printf("%d\n", pn[i]);
return 0;}
int *genNumbers(int size){
int i;int *pn = malloc(4 * size);for (i = 0; i < size; i++)
scanf("%d", &pn[i]);
return pn;}
47
Memory Leakn It occurs when a computer program incorrectly
manages memory allocations.n Memory that is no longer used is not released yet.
48
Solving Memory Leakn Use a pair of allocation and deallocation together!
#include <stdio.h>#include <stdlib.h>void genNumbers(int* pn, int s);
int main(){
int size, i;scanf("%d", &size);int* pn = malloc(4 * size);
genNumbers(pn, size);for (i = 0; i < size; i++)
printf("%d\n", pn[i]);
free(pn);return 0;
}
void genNumbers(int* pn, int s){
int i;for (i = 0; i < s; i++)
scanf("%d", &pn[i]);}
49
What is Structure?n Definition
n A collection of multiple related elementsn A single name including possibly several different types
50
What is Structure?n How to declare a structure
n All elements in the structure should be related logically.
#include <stdio.h>typedef struct{
char name[10];int scores[3];
} STUDENT;
int main(){
STUDENT s1 = { "Alice", 80, 70, 60 };
printf("%s\n", s1.name);for (int i = 0; i < 3; i++)
printf("%d\n", s1.scores[i]);return 0;
}
51
-> (Arrow) Operatorn It is used to access the value of a structure pointer.
#include <stdio.h>typedef struct{
char name[10];int scores[3];
} STUDENT;
int main(){
STUDENT s1 = { "Alice", 80, 70, 60 };STUDENT* s2 = &s1;
printf("%s\n", s2->name);for (int i = 0; i < 3; i++)
printf("%d\n", s2->scores[i]);return 0;
}
52
Example: Structuren Is it a correct code?
int main(){
STUDENT stu[1];for (int i = 0; i < 1; i++) {
scanf("%s", stu[i].name); for (int j = 0; j < 3; j++) {
scanf("%d", &stu[i].scores[j]);stu[i].total += stu[i].scores[j];
}}for (int i = 0; i < 1; i++) {
printf("%s\n", stu[i].name);for (int j = 0; j < 3; j++)
printf("%d\n", stu[i].scores[j]);printf("%d\n", stu[i].total);
}return 0;
}
typedef struct{
char name[10];int scores[3];int total;
} STUDENT;
53
Example: Structuren Structure with dynamic memory allocation
int main(){
int n;scanf("%d", &n);
STUDENT* s = malloc(sizeof(STUDENT)*n);for (int i = 0; i < n; i++) {
scanf("%s", s[i].name);s[i].total = 0;for (int j = 0; j < 3; j++) {
scanf("%d", &s[i].scores[j]);s[i].total += s[i].scores[j];
}}free(s);return 0;
}
typedef struct{
char name[10];int scores[3];int total;
} STUDENT;
54
Example: Structuren Multiplying two fractions
#include <stdio.h>
int main(){
FRACTION f1 = { 4, 5 };FRACTION f2 = { 3, 7 };FRACTION f3;
f3.numerator = f1.numerator * f2.numerator;f3.denominator = f1.denominator * f2.denominator;
printf("%d / %d", f3.numerator, f3.denominator);return 0;
}
typedef struct{int numerator;int denominator;} FRACTION;
55
Example: Structuren Summing two fractions
#include <stdio.h>
int main(){
FRACTION f1 = { 4, 5 };FRACTION f2 = { 3, 7 };FRACTION f3;
f3.numerator = f1.numerator * f2.denominator;f3.numerator += f2.numerator * f1.denominator;f3.denominator = f1.denominator * f2.denominator;
printf("%d / %d", f3.numerator, f3.denominator);return 0;
}
typedef struct{int numerator;int denominator;} FRACTION;
56
How to Be a Good Programmern Tips for programming
n https://www.oreilly.com/ideas/7-ways-to-be-a-better-programmer-in-2014
n �������Websiten Euler project: http://euler.synap.co.kr/n Backjoon online judge: https://www.acmicpc.net/n Algospot: https://www.algospot.com/judge/problem/list/
