HackTrail

What is the output of the following C code?

#include <stdio.h>

int main() {

int arr[] = {1, 3, 5, 7, 9};

int *p = arr;

printf("%d", *(p + 3));

return 0;

}

• • 1

• • 5

• • 7

• • 9

What is the output of this recursive function in Python?

def func(n):

if n == 0:

return 0

return n + func(n - 1)

print(func(5))

• Infinite recursion

• • 5

• • 10

• • 15

What is the output of this Python code?

def dfs(graph, v, visited=set()):

visited.add(v)

for neighbor in graph[v]:

if neighbor not in visited:

dfs(graph, neighbor, visited)

return visited

graph = {'A': ['B'], 'B': ['C'], 'C': ['A']}

print(dfs(graph, 'A'))

• • Error

• • {'A'}

• • {'A', 'C'}

• • {'A', 'B', 'C'}

Time complexity of the following C function?

void fun(int n) {

for (int i = 1; i <= n; i *= 2)

printf("%d ", i);

}

• • O(n)

• • O(log n)

• • O(n log n)

• • O(1)

Output of the Python code:

a = [1, 2, 3]

b = a

b.append(4)

print(a)

• • [1, 2, 3]

• • [1, 2, 3, 4]

• • [1, 2, 4]

• • Error

Which queue implementation allows insertion and deletion at both ends?

• • LinkedList

• • Queue

• • PriorityQueue

• • Dequeue

What does the following C code print?

char str[] = "HackTrail";

printf("%c", *(str + 4));

• T

• r

• a

• k

What is the output of this infix to postfix converter?

#include <stdio.h>

#include <string.h>

#include <ctype.h>

#define MAX 100

char stack[MAX];

int top = -1;

void push(char c) {

stack[++top] = c;

}

char pop() {

return stack[top--];

}

int precedence(char c) {

if (c == '+' || c == '-') return 1;

if (c == '*' || c == '/') return 2;

return 0;

}

void infixToPostfix(char *exp) {

int i;

char ch;

for (i = 0; exp[i]; i++) {

ch = exp[i];

if (isalnum(ch)) {

printf("%c", ch);

} else if (ch == '(') {

push(ch);

} else if (ch == ')') {

while (top != -1 && stack[top] != '(')

printf("%c", pop());

pop(); // Pop '('

} else {

while (top != -1 && precedence(stack[top]) >= precedence(ch))

printf("%c", pop());

push(ch);

}

}

while (top != -1)

printf("%c", pop());

}

int main() {

char exp[] = "a+b*c";

infixToPostfix(exp);

return 0;

}

• • abc*+

• • ab+c*

• • a+bc*

• • abc+*

What is the output of this Python max heap implementation?

import heapq

h = []

heapq.heappush(h, -10)

heapq.heappush(h, -20)

heapq.heappush(h, -5)

print(-heapq.heappop(h))

• • 10

• • 5

• • -20

• • 20

What is the output?

#include <stdio.h>

int main() {

int n = 4, i, j;

for (i = 1; i <= n; i++) {

for (j = 1; j <= i; j++) {

printf("*");

}

printf("\n");

}

return 0;

}

• *

  **

  ***

  ****

• ****

  ***

  **

  *

• *

  *

  *

  *

• ****

  ****

  ****

  ****