Common questions :MCSL 209

1. Stack Implementation Using Two Queues

#include 
#define N 50

int q1[N], q2[N], f1=0,r1=-1,f2=0,r2=-1;

void push(int x){
    q2[++r2]=x;
    while(f1<=r1) q2[++r2]=q1[f1++];
    f1=0; r1=-1;
    for(int i=f2;i<=r2;i++) q1[++r1]=q2[i];
    f2=0; r2=-1;
}

void pop(){
    if(r1<0) printf("Stack Empty\n");
    else printf("Popped: %d\n", q1[f1++]);
}

int main(){
    push(10); push(20); push(30);
    pop(); pop();
}

2. Binary Tree Traversals (Inorder, Preorder, Postorder)

#include 
#include 

struct node{
    int data;
    struct node *l,*r;
};

struct node* new(int x){
    struct node* n=malloc(sizeof(*n));
    n->data=x; n->l=n->r=NULL;
    return n;
}

void inorder(struct node* t){
    if(t){ inorder(t->l); printf("%d ",t->data); inorder(t->r); }
}
void preorder(struct node* t){
    if(t){ printf("%d ",t->data); preorder(t->l); preorder(t->r); }
}
void postorder(struct node* t){
    if(t){ postorder(t->l); postorder(t->r); printf("%d ",t->data); }
}

int main(){
    struct node* root=new(1);
    root->l=new(2); root->r=new(3);
    inorder(root); printf("\n");
    preorder(root); printf("\n");
    postorder(root);
}

3. Prefix to Postfix Conversion

#include 
#include 

char stack[50][50];
int top=-1;

void push(char *s){ strcpy(stack[++top],s); }
char* pop(){ return stack[top--]; }

int isOp(char c){
    return c=='+'||c=='-'||c=='*'||c=='/';
}

int main(){
    char pre[50],op1[50],op2[50],res[50];
    scanf("%s",pre);

    for(int i=strlen(pre)-1;i>=0;i--){
        if(isOp(pre[i])){
            strcpy(op1,pop());
            strcpy(op2,pop());
            sprintf(res,"%s%s%c",op1,op2,pre[i]);
            push(res);
        }else{
            res[0]=pre[i]; res[1]='\0';
            push(res);
        }
    }
    printf("%s",stack[top]);
}

4. Singly Linked List Sort

#include 
#include 

struct node{ int data; struct node* next; };

struct node* add(struct node* h,int x){
    struct node* n=malloc(sizeof(*n));
    n->data=x; n->next=h; return n;
}

void sort(struct node* h){
    for(;h;h=h->next)
        for(struct node* t=h->next;t;t=t->next)
            if(h->data>t->data){
                int x=h->data;
                h->data=t->data;
                t->data=x;
            }
}

void display(struct node* h){
    while(h){ printf("%d ",h->data); h=h->next; }
}

int main(){
    struct node* h=NULL;
    int x;
    while(scanf("%d",&x),x!=-1) h=add(h,x);
    sort(h);
    display(h);
}

5. Elements NOT Common in Two Linked Lists

#include 
#include 

struct node{ int data; struct node* next; };

struct node* add(struct node* h,int x){
    struct node* n=malloc(sizeof(*n));
    n->data=x; n->next=h; return n;
}

int found(struct node* h,int x){
    while(h){ if(h->data==x) return 1; h=h->next; }
    return 0;
}

int main(){
    struct node *A=NULL,*B=NULL;
    int x;
    while(scanf("%d",&x),x!=-1) A=add(A,x);
    while(scanf("%d",&x),x!=-1) B=add(B,x);

    printf("Not common: ");
    for(struct node* p=A;p;p=p->next)
        if(!found(B,p->data)) printf("%d ",p->data);
}

6. Reverse Input String

#include 
#include 

int main(){
    char s[100];
    gets(s);
    for(int i=strlen(s)-1;i>=0;i--)
        printf("%c",s[i]);
}

7. Concatenate Two Strings

#include 
#include 

int main(){
    char a[100],b[50];
    gets(a); gets(b);
    strcat(a,b);
    printf("%s",a);
}