李俊辰 PB23000176
3.7
bool check(char *a){//return true if the expression is legal
stack<char> s;
for(; *a; a++){
if(*a == ')'){
if(s.top() != '('){
return false;
}
s.pop();
}
else if(*a == ']'){
if(s.top() != '['){
return false;
}
s.pop();
}
else if(*a == '}'){
if(s.top() != '{'){
return false;
}
s.pop();
}
else if(*a == '(' || *a == '[' || *a == '{'){
s.push(*a);
}
else{
return false;
}
}
return s.empty();
}
3.8
int level(char c){
if(c == '+' || c == '-'){
return 1;
}
else if(c == '*' || c == '/'){
return 2;
}
return 0;
}
void trans(char *a, char *t){
stack<char> s;
for(; *a; a++){
if(*a >= 'a' && *a <= '9'){
*t++ = *a;
}
for(;;){
if(*a == '(' || s.empty() || level(*a) > level(s.top())){
s.push(*a);
break;
}
char now = s.top();
s.pop();
if(now != '('){
*t++ = now;
}
else{
break;
}
}
}
while(!s.empty()){
*t++ = s.top();
s.pop();
}
}
3.9
double calc(char *a){
stack<double> s;
double x, y, z;
bool ff = false;
for(; *a; a++){
if(*a == '+' || *a == '-' || *a == '*' || *a == '/'){
ff = false;
x = s.top();
s.pop();
y = s.top();
s.pop();
}
if(*a == '+'){
s.push(x+y);
}
else if(*a == '-'){
s.push(x-y);
}
else if(*a == '*'){
s.push(x*y);
}
else if(*a == '/'){
s.push(x/y);
}
else if(*a >= '0' && *a <= '9'){
ff = true;
z = z*10+(*a-'0');
}
else if(*a == ' ' && ff){
ff = false;
s.push(z);
}
}
return s.top();
}
3.10
void init(Queue *q){
q->tail = NULL;
}
void push(Queue *q, Node x){
QueueNode *t = new QueueNode;
t->value = x;
if(!q->tail){
t->next = t;
q->tail = t;
return;
}
t->next = q->tail->next;
q->tail->next = t;
q->tail = t;
}
Node pop(Queue *q){
if(q->tail->next == q->tail){
Node ans = q->tail->value;
delete q->tail;
q->tail = NULL;
return ans;
}
QueueNode ans = *(q->tail->next);
delete q->tail->next;
q->tail->next = ans->next;
return ans->value;
}
3.11
void push(Queue *q, Node x){
}