The document provides a detailed overview of stacks and queues, including their definitions, structures, and various operations such as adding and deleting elements. It highlights applications of these data structures in recursion, expression evaluation, and job scheduling, as well as methods for converting infix expressions to postfix notation. Additionally, it discusses the theoretical aspects of operator precedence and associativity in programming languages.

1. 1
STACKS AND QUEUES
UNIT 2
UNIT 2

2. CHAPTER 3 2
Token Operator Precedence Associativity
()
[]
-> .
Function call
Array element
Struct or union member
17
17
17
Left-to-right
i-- i++ Increment, decrement 16 Left-to-right
--I ++i
!
~
- +
& *
Sizeof
Decrement, increment
Logical not
One’s complement
Unary minus or plus
Address or indirection
Size (in bytes)
15 Right- to-left
(type) Type cast 14 Right- to-left
* / % Multiplicative 13 Left-to-right
+ - Binary add or subtract 12 Left-to-right
<< >> Shift 11 Left-to-right

3. CHAPTER 3 3
> >=
< <=
Relational 10 Left-to-
right
== != Equality 9 Left-to-
right
& Bitwise and 8 Left-to-
right
^ Bitwise exclusive or 7 Left-to-
right
| Bitwise or 6 Left-to-
right
&& Logical and 5 Left-to-
right
|| Logical or 4 Left-to-
right
?: Conditional 3 Right- to-
left
= += -= /= *=
%= <<= >>= &=
^= |=
Assignment 2 Right- to-
left
. comma 1 Left-to-
right
*Figure 3.12: Precedence hierarchy for C (p.130)

4. CHAPTER 3 4
Stack (stack: a Last-In-First-Out (LIFO) list )
Stack
An ordered list
Insertions and deletions are made at one end, called top
Illustration
Inserting and deleting elements in a stack
A
B
A
C
B
A
D
C
B
A
E
D
C
B
A
D
C
B
A
top
top
top
top
top
top
push push pop

5. CHAPTER 3 5
Some stack applications
Implementing recusive call
Expression evaluation
Infix to postfix
Postfix evaluation
Maze problem
Breadth First Search
……

6. CHAPTER 3 6
old frame pointer
return address
fp
main
fp
al
(a) (b)
*Figure 3.2: System stack after function call a1 (p.109)
old frame pointer
return address
local variables
old frame pointer
return address
an application of stack: stack frame of function call
system stack before a1 is invoked system stack after a1 is invoked
fp: a pointer to current stack frame

7. CHAPTER 3 7
structure Stack is
objects: a finite ordered list with zero or more elements.
functions:
for all stack  Stack, item  element, max_stack_size
 positive integer
Stack CreateS(max_stack_size) ::=
create an empty stack whose maximum size is
max_stack_size
Boolean IsFull(stack, max_stack_size) ::=
if (number of elements in stack == max_stack_size)
return TRUE
else return FALSE
Stack Add(stack, item) ::=
if (IsFull(stack)) stack_full
else insert item into top of stack and return
abstract data type for stack

8. CHAPTER 3 8
Boolean IsEmpty(stack) ::=
if(stack == CreateS(max_stack_size))
return TRUE
else return FALSE
Element Delete(stack) ::=
if(IsEmpty(stack)) return
else remove and return the item on
the top of the stack.
*ADT 3.1: Abstract data type Stack (p.109)

9. CHAPTER 3 9
Stack CreateS(max_stack_size) ::=
#define MAX_STACK_SIZE 100 /* maximum stack size */
typedef struct {
int key;
/* other fields */
} element;
element stack[MAX_STACK_SIZE];
int top = -1;
Boolean IsEmpty(Stack) ::= top< 0;
Boolean IsFull(Stack) ::= top >= MAX_STACK_SIZE-1;
Implementation: using array

10. CHAPTER 3 10
void add(int *top, element item)
{
if (*top >= MAX_STACK_SIZE-1) {
stack_full( );
return;
}
stack[++*top] = item;
}
*program 3.1: Add to a stack (p.111)
Add to a stack

11. CHAPTER 3 11
element delete(int *top)
{
if (*top == -1)
return stack_empty( ); /* returns and error key */
return stack[(*top)--];
}
*Program 3.2: Delete from a stack (p.111)
Delete from a stack

12. CHAPTER 3 12
Queue (Queue: a First-In-First-Out (FIFO) list)
Queue
An ordered list
All insertions take place at one end, rear
rear
All deletions take place at the opposite end, front
front
Illustration
A
B
A
C
B
A
D
C
B
A
D
C
B
rear
front
rear
front
rear
front
rear
front
rear
front

13. CHAPTER 3 13
Some queue applications
Job scheduling
Event list in simulator
Server and Customs
……

14. CHAPTER 3 14
front rear Q[0] Q[1] Q[2] Q[3] Comments
-1
-1
-1
-1
0
1
-1
0
1
2
2
2
J1
J1 J2
J1 J2 J3
J2 J3
J3
queue is empty
Job 1 is added
Job 2 is added
Job 3 is added
Job 1 is deleted
Job 2 is deleted
*Figure 3.5: Insertion and deletion from a sequential queue (p.117)
Application: Job scheduling

15. CHAPTER 3 15
structure Queue is
objects: a finite ordered list with zero or more elements.
functions:
for all queue  Queue, item  element,
max_ queue_ size  positive integer
Queue CreateQ(max_queue_size) ::=
create an empty queue whose maximum size is
max_queue_size
Boolean IsFullQ(queue, max_queue_size) ::=
if(number of elements in queue == max_queue_size)
return TRUE
else return FALSE
Queue AddQ(queue, item) ::=
if (IsFullQ(queue)) queue_full
else insert item at rear of queue and return queue
Queue (ADT)

16. CHAPTER 3 16
Boolean IsEmptyQ(queue) ::=
if (queue ==CreateQ(max_queue_size))
return TRUE
else return FALSE
Element DeleteQ(queue) ::=
if (IsEmptyQ(queue)) return
else remove and return the item at front of
queue.
*ADT 3.2: Abstract data type Queue (p.115)

17. CHAPTER 3 17
Queue CreateQ(max_queue_size) ::=
# define MAX_QUEUE_SIZE 100/* Maximum queue size */
typedef struct {
int key;
/* other fields */
} element;
element queue[MAX_QUEUE_SIZE];
int rear = -1;
int front = -1;
Boolean IsEmpty(queue) ::= front == rear
Boolean IsFullQ(queue) ::= rear == MAX_QUEUE_SIZE-1
Implementation 1: using array

18. CHAPTER 3 18
void addq(int *rear, element item)
{
if (*rear == MAX_QUEUE_SIZE_1) {
queue_full( );
return;
}
queue [++*rear] = item;
}
*Program 3.3: Add to a queue (p.108) (1/e)
Add to a queue

19. CHAPTER 3 19
element deleteq(int *front, int rear)
{
if ( *front == rear)
return queue_empty( ); /* return an error key */
return queue [++ *front];
}
*Program 3.4: Delete from a queue(p.108) (1/e)
Delete from a queue

20. CHAPTER 3 20
*Figure 3.6: Empty and nonempty circular queues (p.117)
Implementation 2: regard an array as a circular queue
front: one position counterclockwise from the first element
rear: current end
front = 0
rear = 0
[0]
[1]
[2] [3]
[4]
[5]
Empty circular Queue
front = 0
rear = 3
[0]
[1]
[2] [3]
[4]
[5]
J1
J2 J3
Nonempty circular queue

21. CHAPTER 3 21
*Figure 3.7: Full circular queues and then we remove the item (p.110)
(1/e)
Problem: one space is left when queue is full
front = 0
rear = 5
[0]
[1]
[2] [3]
[4]
[5]
J1
J2 J3
J4
J5
front = 4
rear = 3
[0]
[1]
[2] [3]
[4]
[5]
J7
J8 J9
J6 J5
Full Circular queue
(waste one space )

22. CHAPTER 3 22
避免出現 rear=front 而無法分辨 circular
queue 是滿的 ? 還是空的 ? 所以最多存
放 Maxsize -1 個空間
或是加入一個 COUNT 變數表示 queue
的個數 COUNT=0 ( 空 )
COUNT=Maxsize ( 滿 )

23. CHAPTER 3 23
void addq(int front, int *rear, element item)
{
*rear = (*rear +1) % MAX_QUEUE_SIZE;
if (front == *rear) /* reset rear and print error */
return;
}
queue[*rear] = item;
}
*Program 3.5: Add to a circular queue (p.110) (1/e)
Add to a circular queue

24. CHAPTER 3 24
element deleteq(int* front, int rear)
{
element item;
if (*front == rear)
return queue_empty( );
/* queue_empty returns an error key */
*front = (*front+1) % MAX_QUEUE_SIZE;
return queue[*front];
}
*Program 3.6: Delete from a circular queue (p.111) (1/e)
Delete from a circular queue

25. CHAPTER 3 25
Evaluation of Expressions
Evaluating a complex expression in computer
((rear+1==front)||((rear==MaxQueueSize-1)&&!
front))
x= a/b- c+ d*e- a*c
Figuring out the order of operation within any
expression
A precedence hierarchy within any programming
language
See Figure 3.12

26. CHAPTER 3 26
Evaluation of Expressions (Cont.)
Ways to write expressions
Infix (standard)
Prefix
Postfix
compiler, a parenthesis-free notation
Infix Postfix
2+3*4 2 3 4*+
a*b+5 ab*5+
(1+2)*7 1 2+7*
a*b/c ab*c/
((a/(b-c+d))*(e-a)*c abc-d+/ea-*c*
a/b-c+d*e-a*c ab/c-de*+ac*-

27. CHAPTER 3 27
Evaluation of Postfix Expressions
• Left-to-right scan Postfix expression,
1) Stack operands
operands until find an operator,
2) Meet operator, remove correct operands for
this operator,
3) Perform the operation,
4) Stack the result
• Remove the answer from the top of stack

28. CHAPTER 3 28
Token Stack
Stack Top
[0] [1] [2]
6 6 0
2 6 2 1
/ 6/2 0
3 6/2 3 1
- 6/2-3 0
4 6/2-3 4 1
2 6/2-3 4 2 2
* 6/2-3 4*2 1
+ 6/2-3+4*2 0
Postfix evaluation of 6 2/3-4 2*+
6 2/3-4 2*+
Evaluation of Postfix Expressions

29. CHAPTER 3 29
#define MAX_STACK_SIZE 100
#define MAX_EXPR_SIZE 100 /* max size of expression */
typedef enum{1paran, rparen, plus, minus, times, divide,
mod, eos, operand} precedence;
int stack[MAX_STACK_SIZE]; /* global stack */
char expr[MAX_EXPR_SIZE]; /* input string */
Assumptions:
operators: +, -, *, /, %
operands: single digit integer

30. CHAPTER 3 30
int eval(void)
{
precedence token;
char symbol;
int op1, op2;
int n = 0; /* counter for the expression string */
int top = -1;
token = get_token(&symbol, &n);
while (token != eos) {
if (token == operand)
add(&top, symbol-’0’); /* stack add */
exp: character array

31. CHAPTER 3 31
else {
/* remove two operands, perform operation, and
return result to the stack */
op2 = delete(&top); /* stack delete */
op1 = delete(&top);
switch(token) {
case plus: add(&top, op1+op2); break;
case minus: add(&top, op1-op2); break;
case times: add(&top, op1*op2); break;
case divide: add(&top, op1/op2); break;
case mod: add(&top, op1%op2);
}
}
token = get_token (&symbol, &n);
}
return delete(&top); /* return result */
}
*Program 3.9: Function to evaluate a postfix expression (p.122)

32. CHAPTER 3 32
precedence get_token(char *symbol, int *n)
{
*symbol =expr[(*n)++];
switch (*symbol) {
case ‘(‘ : return lparen;
case ’)’ : return rparen;
case ‘+’: return plus;
case ‘-’ : return minus;
case ‘/’ : return divide;
case ‘*’ : return times;
case ‘%’ : return mod;
case ‘0‘ : return eos;
default : return operand;
}
}
*Program 3.10: Function to get a token from the input string (p.123)

33. CHAPTER 3 33
Infix to Postfix
1) Method I
1) Fully parenthesize the expression
2) Move all binary operators so that they replace their
corresponding right parentheses
3) Delete all parentheses
 Examples:a/b-c+d*e-a*c
 ((((a/b)-c)+(d*e))-(a*c)), fully parentheses
 ab/
/c-
-de*+
*+ac*-
*-, replace right parentheses and delete
all parentheses
 Disadvantage
 inefficient, two passes

34. CHAPTER 3 34
Infix to Postfix
 Method II
1) scan the infix expression left-to-right
2) output operand encountered
3) output operators depending on their precedence, i.e.,
higher precedence operators first
 Example: a+b*c
a+b*c, simple expression
Token Stack Top Output
[0] [1] [2]
a -1 a
+ + 0 a
b + 0 ab
* + * 1 ab
c + * 1 abc
eos -1 abc*+

35. CHAPTER 3 35
Infix to Postfix
Example: a*(b+c)*d , parenthesized expression
Token Stack Top Output
[0] [1] [2]
a -1 a
* * 0 a
( * ( 1 a
b * ( 1 ab
+ * ( + 2 ab
c * ( + 2 abc
) * 0 abc+
* * 0 abc+*
d * 0 abc+*d
eos * 0 abc+*d*

36. CHAPTER 3 36
Infix to Postfix
Last two examples suggests a precedence-based scheme
for stacking and unstacking operators
isp (in-stack precedence)
icp (in-coming precedence)
precedence stack[MaxStackSize];
/* isp and icp arrays - index is value of precedence
lparen, rparen, plus, minus, time divide, mod, eos */
static int isp[]= { 0, 19, 12, 12, 13, 13, 13, 0};
static int icp[]= {20, 19, 12, 12, 13, 13, 13, 0};
 See program 3.11- (n)

37. CHAPTER 3 37
void postfix(void)
{
/* output the postfix of the expression. The expression
string, the stack, and top are global */
char symbol;
precedence token;
int n = 0;
int top = 0; /* place eos on stack */
stack[0] = eos;
for (token = get _token(&symbol, &n); token != eos;
token = get_token(&symbol, &n)) {
if (token == operand)
printf (“%c”, symbol);
else if (token == rparen ){

38. CHAPTER 3 38
/*unstack tokens until left parenthesis */
while (stack[top] != lparen)
print_token(delete(&top));
delete(&top); /*discard the left parenthesis */
}
else{
/* remove and print symbols whose isp is greater
than or equal to the current token’s icp */
while(isp[stack[top]] >= icp[token] )
print_token(delete(&top));
add(&top, token);
}
}
while ((token = delete(&top)) != eos)
print_token(token);
print(“n”);
}
*Program 3.11: Function to convert from infix to postfix (p.126)
(n)
f(n)=(g(n)) iff there exist
positive
constants c1, c2, and n0 such
that c1g(n)f(n)c2g(n) for all
n, nn0.
f(n)=(g(n)) iff g(n) is both an
upper and lower bound on f(n).

39. CHAPTER 3 39
*Figure 3.17: Infix and postfix expressions (p.127)
(1) evaluation
(2) transformation
後序優於中序 :
去除運算子優先權 , 結合性和括號
方便 complier 計算運算子的值 , 掃描一次便可求結果
Infix Prefix
a*b/c
a/b-c+d*e-a*c
a*(b+c)/d-g
/*abc
-+-/abc*de*ac
-/*a+bcdg

40. CHAPTER 3 40
Multiple stacks and queues
Two stacks
m[0], m[1], …, m[n-2], m[n-1]
bottommost bottommost
stack 1 stack 2
More than two stacks (n)
memory is divided into n equal segments
boundary[stack_no]
0  stack_no < MAX_STACKS
top[stack_no]
0  stack_no < MAX_STACKS

41. CHAPTER 3 41
boundary[ 0] boundary[1] boundary[ 2] boundary[n]
top[ 0] top[ 1] top[ 2]
All stacks are empty and divided into roughly equal segments.
*Figure 3.18: Initial configuration for n stacks in memory [m]. (p.140)
0 1 [ m/n ] 2[ m/n ] m-1
Initially, boundary[i]=top[i].

42. CHAPTER 3 42
#define MEMORY_SIZE 100 /* size of memory */
#define MAX_STACK_SIZE 100
/* max number of stacks plus 1 */
/* global memory declaration */
element memory[MEMORY_SIZE];
int top[MAX_STACKS];
int boundary[MAX_STACKS];
int n; /* number of stacks entered by the user */
p.139
top[0] = boundary[0] = -1;
for (i = 1; i < n; i++)
top[i] =boundary[i] =(MEMORY_SIZE/n)*i;
boundary[n] = MEMORY_SIZE-1;
p.139

43. CHAPTER 3 43
void add(int i, element item)
{
/* add an item to the ith stack */
if (top[i] == boundary [i+1])
stack_full(i); may have unused storage
memory[++top[i]] = item;
}
*Program 3.12:Add an item to the stack stack-no (p.129)
element delete(int i)
{
/* remove top element from the ith stack */
if (top[i] == boundary[i])
return stack_empty(i);
return memory[top[i]--];
}
*Program 3.13:Delete an item from the stack stack-no (p.130)

44. CHAPTER 3 44
b[0] t[0] b[1] t[1] b[i] t[i] t[i+1] t[j] b[j+1] b[n]
b[i+1] b[i+2]
b=boundary, t=top
*Figure 3.19: Configuration when stack i meets stack i+1,
but the memory is not full (p.141)
Find j, stack_no < j < n
such that top[j] < boundary[j+1]
or, 0  j < stack_no
meet
往左或右找一個空間
( 往左 )
( 往右 )

45. CHAPTER 3 45
0 1 0 0 0 1 1 0 0 0 1 1 1 1 1
1 0 0 0 1 1 0 1 1 1 0 0 1 1 1
0 1 1 0 0 0 0 1 1 1 1 0 0 1 1
1 1 0 1 1 1 1 0 1 1 0 1 1 0 0
1 1 0 1 0 0 1 0 1 1 1 1 1 1 1
0 0 1 1 0 1 1 1 0 1 0 0 1 0 1
0 1 1 1 1 0 0 1 1 1 1 1 1 1 1
0 0 1 1 0 1 1 0 1 1 1 1 1 0 1
1 1 0 0 0 1 1 0 1 1 0 0 0 0 0
0 0 1 1 1 1 1 0 0 0 1 1 1 1 0
0 1 0 0 1 1 1 1 1 0 1 1 1 1 0
entrance
exit
*Figure 3.8: An example maze(p.123)
A Mazing Problem
1: blocked path 0: through path

46. CHAPTER 3 46
NW
[row-1][col-1]
N
[row-1][col]
NE
[row-1][col+1]
W
[row][col-1] 
[row][col]
E
[row][col+1]
SW
[row+1][col-1]
S
[row+1][col]
SE
[row+1][col+1]
*Figure 3.9: Allowable moves (p.124)
a possible representation

47. CHAPTER 3 47
typedef struct {
short int vert;
short int horiz;
} offsets;
offsets move[8]; /*array of moves for each direction*/
a possible implementation
Name Dir move[dir].vert move[dir].horiz
N
NE
E
SE
S
SW
W
NW
0
1
2
3
4
5
6
7
-1
-1
0
1
1
1
0
-1
0
1
1
1
0
-1
-1
-1
next_row = row + move[dir].vert;
next_col = col + move[dir].horiz;
*Figure 3.10 : Table of moves
(p.124)

48. CHAPTER 3 48
#define MAX_STACK_SIZE 100
/* maximum stack size */
typedef struct {
short int row;
short int col;
short int dir;
} element;
element stack[MAX_STACK_SIZE];
Use stack to keep pass history

49. CHAPTER 3 49
Initialize a stack to the maze’s entrance coordinates and direction to north;
while (stack is not empty){
/* move to position at top of stack */
<row, col, dir> = delete from top of stack;
while (there are more moves from current position) {
<next_row, next_col > = coordinates of next move;
dir = direction of move;
if ((next_row == EXIT_ROW)&& (next_col == EXIT_COL))
success;
if (maze[next_row][next_col] == 0 &&
mark[next_row][next_col] == 0) {

50. CHAPTER 3 50
/* legal move and haven’t been there */
mark[next_row][next_col] = 1;
/* save current position and direction */
add <row, col, dir> to the top of the stack;
row = next_row;
col = next_col;
dir = north;
}
}
}
printf(“No path foundn”);
*Program 3.11: Initial maze algorithm (p.126)

51. CHAPTER 3 51
000001
111110
100001
011111
100001
111110
100001
011111
100000
*Figure 3.11: Simple maze with a long path (p.127)
The size of a stack?
m*p

52. CHAPTER 3 52
void path (void)
{
/* output a path through the maze if such a path exists */
int i, row, col, next_row, next_col, dir, found = FALSE;
element position;
mark[1][1] = 1; top =0;
stack[0].row = 1; stack[0].col = 1; stack[0].dir = 1;
while (top > -1 && !found) {
position = delete(&top);
row = position.row; col = position.col;
dir = position.dir;
while (dir < 8 && !found) {
/*move in direction dir */
next_row = row + move[dir].vert;
next_col = col + move[dir].horiz;

53. CHAPTER 3 53
if (next_row==EXIT_ROW && next_col==EXIT_COL)
found = TRUE;
else if ( !maze[next_row][next_col] &&
!mark[next_row][next_col] {
mark[next_row][next_col] = 1;
position.row = row; position.col = col;
position.dir = ++dir;
add(&top, position);
row = next_row; col = next_col; dir = 0;
}
else ++dir;
}
}

54. CHAPTER 3 54
if (found) {
printf(“The path is :n”);
printf(“row coln”);
for (i = 0; i <= top; i++)
printf(“ %2d%5d”, stack[i].row, stack[i].col);
printf(“%2d%5dn”, row, col);
printf(“%2d%5dn”, EXIT_ROW, EXIT_COL);
}
else printf(“The maze does not have a pathn”);
}
*Program 3.12:Maze search function (p.128)