Qualcomm interview prep

DSAMedium

The sorted array [4, 5, 6, 7, 0, 1, 2] has been rotated. A modified binary search looks for 0. Why can binary search still work, and how fast is it?

1. At every step at least one half of the range is sorted, which tells you which half can hold the target; O(log n)
2. You must scan for the rotation point, so it is O(n) at best
3. The array must be sorted again first, so it takes O(n log n)
4. It only works when the array has not been rotated

This topic is named in a candidate’s interview report: On-campus interview, 2023, on GeeksforGeeks.

DSAEasy

Two pointers start at the head of a singly linked list. Each step, one moves one node and the other moves two. When the fast one reaches the end, where is the slow one?

1. At the head
2. At the middle node
3. At the last node
4. At the second node

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

DSAHard

Bars have heights [0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]. How many units of rain water are trapped between them?

1. 5
2. 7
3. 8
4. 6

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

DSAMedium

How many palindromic substrings does "aaa" have, counting each starting position separately?

1. 6
2. 4
3. 3
4. 5

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

C and C++Medium

What does this print?

#include <stdio.h>

int main(void) {
    int n = 29;      /* 11101 in binary */
    int k = 2;
    printf("%d", n & ~(1 << k));
    return 0;
}

1. 25
2. 29
3. 27
4. 21

This topic is named in a candidate’s interview report: Fresher off-campus interview, 2021, on GeeksforGeeks.

C and C++Medium

In C, what do int *a[9]; and int (*b)[9]; declare?

1. Both are arrays of 9 pointers to int
2. Both are pointers to an array of 9 ints
3. a is a pointer to an array of 9 ints; b is an array of 9 pointers to int
4. a is an array of 9 pointers to int; b is a pointer to an array of 9 ints

This topic is named in a candidate’s interview report: Fresher off-campus interview, 2021, on GeeksforGeeks.

C and C++Easy

How does calloc(n, size) differ from malloc(n * size)?

1. calloc sets every byte of the block to zero; malloc leaves the contents undefined
2. malloc zeroes the memory and calloc does not
3. calloc allocates on the stack
4. calloc can only allocate arrays of int

This topic is named in a candidate’s interview report: Fresher off-campus interview, 2021, on GeeksforGeeks.

C and C++Medium

You copy 8 bytes from buf to buf + 2 in the same array, so the source and destination overlap. Which C function is guaranteed to copy correctly?

1. memmove, which behaves as if the bytes went through a temporary buffer
2. memcpy, because it is faster
3. Both memcpy and memmove
4. Neither; overlapping copies cannot be done in C

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

C and C++Medium

Why would C code declare a memory-mapped hardware status register as volatile?

1. So it is placed in read-only memory
2. So every access is atomic and thread-safe
3. So it is zero-initialised at start-up
4. So the compiler reads it from memory on every access instead of keeping it in a register or removing reads it thinks are redundant

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

C and C++Medium

What does this print?

#include <stdio.h>
#include <stdlib.h>

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

struct node *insert(struct node *head, int v) {
    struct node *n = malloc(sizeof *n);
    n->v = v;
    if (head == NULL || v < head->v) { n->next = head; return n; }
    struct node *p = head;
    while (p->next && p->next->v < v) p = p->next;
    n->next = p->next;
    p->next = n;
    return head;
}

int main(void) {
    struct node *h = NULL;
    int xs[] = {5, 1, 4, 2};
    for (int i = 0; i < 4; i++) h = insert(h, xs[i]);
    for (struct node *p = h; p; p = p->next) printf("%d ", p->v);
    return 0;
}

1. 5 1 4 2
2. 1 2 4 5
3. 5 4 2 1
4. 1 4 2 5

This topic is named in a candidate’s interview report: Embedded intern interview, 2026, on Reddit.

Operating systemsMedium

How does a mutex differ from a counting semaphore?

1. A mutex lets one holder in at a time and is released by its owner; a semaphore allows up to N and anyone may signal it
2. They are two names for the same thing
3. A semaphore can only be used between processes
4. A mutex lets N threads in at once

This topic is named in a candidate’s interview report: Fresher off-campus interview, 2021, on GeeksforGeeks.

Operating systemsMedium

A low-priority task holds a lock that a high-priority task needs, while a medium-priority task keeps pre-empting the low one. What is this, and what is a standard fix?

1. Priority inversion; priority inheritance temporarily raises the lock holder to the waiting task's priority
2. Deadlock; kill one of the tasks
3. Starvation; give every task the same priority
4. Thrashing; add more memory

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

Operating systemsEasy

Which component translates a virtual address into a physical address on each memory access?

1. The memory management unit (MMU), using the page table and caching recent translations in the TLB
2. The compiler
3. The linker
4. The disk controller

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

Operating systemsEasy

Which order runs from fastest to slowest?

1. RAM, CPU cache, SSD
2. SSD, RAM, CPU cache
3. CPU cache, SSD, RAM
4. CPU cache, RAM, SSD

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.

AptitudeMedium

100 bulbs start off. In round i, for i from 1 to 100, you toggle every i-th bulb. How many bulbs are on at the end?

1. 50
2. 0
3. 10
4. 1

This topic is named in a candidate’s interview report: Off-campus interview, 2021, on GeeksforGeeks.