Qualcomm C Programming with DSA Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About Qualcomm hiring for C Programming with DSA roles
Qualcomm designs semiconductors and wireless technologies, including Snapdragon processors, modems and connectivity chips for smartphones, PCs, automotive and IoT. Its India centres in Hyderabad and Bengaluru are major engineering sites for software, hardware and testing. It hires for embedded software engineers, test engineers, hardware engineers and data roles.
For C Programming with DSA roles, this Qualcomm practice set focuses most on Stacks, Queues and Hashing (7), Trees and Graphs (6), Pointers and Memory Management (4), Arrays and Strings (3). It has 4 easy, 22 medium, 4 hard questions, so you can start easy and work up to the harder ones.
Company type
Hardware & semiconductors
Headquarters
San Diego, California, USA
Main India offices
Hyderabad, Bengaluru, Chennai
Qualcomm C Programming with DSA interview process
Online assessment (aptitude + technical + coding)
Technical round 1
Technical round 2
Managerial round
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
Solved for QualcommStart practicing
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01
What is a trie and when is it better than a hash table?
A trie is a tree where each edge represents a character, so words sharing a prefix share a path. Lookup and insert take O(L) for a word of length L, independent of how many words are stored. It beats a hash table for prefix queries such as autocomplete, spell checking and longest prefix matching in IP routing. The trade-off is higher memory use from many child pointers.
Track the best sum ending here and the overall best.
long maxSubarray(const int *a, int n) {
long cur = a[0], best = a[0];
for (int i = 1; i < n; i++) {
cur = (cur + a[i] > a[i]) ? cur + a[i] : a[i];
if (cur > best) best = cur;
}
return best;
}
Input {-2, 1, -3, 4, -1, 2, 1, -5, 4} returns 6 for subarray 4, -1, 2, 1.
03
How do you set, clear and toggle a particular bit in C?
Use bit masks with shift operators.
x |= (1u << n); // set bit n
x &= ~(1u << n); // clear bit n
x ^= (1u << n); // toggle bit n
int bit = (x >> n) & 1u; // read bit n
Use unsigned types so shifts are well defined. These operations are common in embedded code for configuring hardware registers.
Alignment means placing data at addresses that are multiples of its size or required boundary, such as 4 for int. CPUs read aligned data faster, and some architectures fault on misaligned access. Compilers add padding in structs to align members. You can check alignment with _Alignof and request it with _Alignas or aligned_alloc in C11.
05
Your stack implementation crashes with deep recursion converted to an explicit stack. What would you check?
Check for stack overflow of your own array: push must verify top < capacity and either fail or grow the array with realloc. Check pop on an empty stack returns an error instead of reading index -1. If using realloc, make sure no pointers into the old buffer are kept. Add asserts in debug builds and test with the largest expected input.
06
How would you check whether a binary tree is a valid BST?
Comparing each node only with its children is wrong, because a deeper node can break the rule. Pass a valid range down: the left child must be in (min, node value) and the right child in (node value, max), starting with the full range of long long. Alternatively, do an in-order traversal and check values are strictly increasing. Both are O(n).
07
Evaluate a postfix expression of single digit numbers using a stack.
Push digits and apply operators to the top two values.
int evalPostfix(const char *s) {
int st[100], top = -1;
for (; *s; s++) {
if (isdigit((unsigned char)*s)) st[++top] = *s - '0';
else if (strchr("+-*/", *s)) {
int b = st[top--], a = st[top--];
switch (*s) {
case '+': st[++top] = a + b; break;
case '-': st[++top] = a - b; break;
case '*': st[++top] = a * b; break;
case '/': st[++top] = a / b; break;
}
}
}
return st[top];
}
23*5+ evaluates to 11.
08
What is a ring buffer and why is it common in embedded systems?
A ring buffer is a fixed-size circular queue in a static array. It needs no dynamic allocation, has O(1) operations and predictable memory, which suits microcontrollers. A single producer, such as a UART interrupt, writes at head while a single consumer, such as the main loop, reads at tail. With power of two sizes, index masking is cheap, and with one writer and one reader it can be lock free.
In expressions, types smaller than int, like char and short, are promoted to int before arithmetic. In mixed signed and unsigned comparisons, the signed value may convert to unsigned. So if (-1 < sizeof(int)) is false, because -1 becomes a huge unsigned number. These rules cause subtle bugs in embedded and systems code, so compile with -Wall -Wextra and use explicit casts carefully.
10
You must schedule the maximum number of non-overlapping meetings in one room. What algorithm do you use?
This is activity selection, solved greedily. Sort meetings by end time, then pick each meeting whose start is not earlier than the end of the last picked one. Choosing the earliest finishing meeting always leaves the most room for the rest, which can be proven by an exchange argument. Sorting dominates, giving O(n log n) time.
11
Implement a circular queue with enqueue and dequeue in C.
A single block is cache friendly and easy to free.
int (*grid)[cols] = malloc(rows * sizeof *grid);
if (!grid) return -1;
grid[2][3] = 5;
free(grid);
// array of row pointers alternative
int **m = malloc(rows * sizeof *m);
for (int i = 0; i < rows; i++)
m[i] = calloc(cols, sizeof **m);
for (int i = 0; i < rows; i++) free(m[i]);
free(m);
The first form uses a variable length array type.
A topological sort orders the vertices of a directed acyclic graph so every edge goes from earlier to later. Kahn's algorithm repeatedly removes vertices with zero in-degree using a queue; DFS adds vertices to the order after finishing their descendants. If not all vertices are processed, the graph has a cycle. It is used for build systems, course prerequisites and task scheduling.
14
Insert a node at the end of a singly linked list using a double pointer.
A pointer to pointer handles the empty list without special cases.
int append(Node **head, int value) {
Node *n = malloc(sizeof *n);
if (!n) return -1;
n->data = value;
n->next = NULL;
while (*head) head = &(*head)->next;
*head = n;
return 0;
}
Call it as append(&head, 5). Keep a tail pointer if you append often.
15
You need to look up 10 lakh user ids quickly in a C program. What structure do you choose?
A hash table gives O(1) average lookup. Size it so the load factor stays under about 0.7, choose a good hash for the key type and use open addressing for better cache behaviour. If ids are dense integers in a known range, a plain array or bitmap is even faster. If the data is static, a sorted array with binary search is simple and memory efficient at O(log n).
16
What is a binary search tree and what are its operation costs?
A binary search tree keeps every node's left subtree smaller and right subtree larger than the node. Search, insert and delete follow one path from the root, so they cost O(h), where h is the height. A balanced tree has h of about log n, but inserting sorted data creates a skewed tree with h equal to n. In-order traversal of a BST gives keys in sorted order.
17
What is a hash table and how are collisions handled?
A hash table maps keys to array slots using a hash function, giving O(1) average insert, search and delete. Collisions happen when two keys map to the same slot. Separate chaining stores a linked list per slot. Open addressing probes for another free slot using linear probing, quadratic probing or double hashing. Keep the load factor low and resize when it grows to maintain speed.
18
What are the basic data types in C and their typical sizes?
C has char (1 byte), short (usually 2), int (usually 4), long (4 on Windows, 8 on 64-bit Linux), long long (at least 8), float (4) and double (8). The standard only fixes minimum ranges, so sizes depend on the platform. Use sizeof to check and the fixed-width types from stdint.h such as int32_t and uint8_t when exact sizes matter.
19
How do you convert an infix expression to postfix?
Use the shunting yard algorithm with an operator stack. Output operands directly. For an operator, pop operators of higher precedence, or equal precedence if left associative, to the output, then push it. Push '(' and on ')' pop until the matching '('. At the end, pop all remaining operators. For example a + b * c becomes a b c * +. Postfix is easy to evaluate with a stack.
20
Rotate an array to the right by k positions in O(n) time and O(1) space.
Use three reversals.
void rev(int *a, int l, int r) {
while (l < r) { int t = a[l]; a[l++] = a[r]; a[r--] = t; }
}
void rotate(int *a, int n, int k) {
k %= n;
if (k == 0) return;
rev(a, 0, n - 1);
rev(a, 0, k - 1);
rev(a, k, n - 1);
}
For 1 2 3 4 5 with k = 2 the result is 4 5 1 2 3.
21
Use a tagged union to store either an int, a float or a string value.
An adjacency matrix is a V by V array where cell [u][v] marks an edge; it gives O(1) edge checks but uses O(V squared) memory, suiting dense graphs. An adjacency list stores for each vertex a list or dynamic array of neighbours, using O(V + E) memory, which suits sparse real world graphs like road or social networks. Weighted graphs store the weight with each edge.
23
Write a C program that counts lines, words and characters in a file.
Read character by character with fgetc.
FILE *fp = fopen(path, "r");
if (!fp) { perror("fopen"); return 1; }
long lines = 0, words = 0, chars = 0;
int c, inWord = 0;
while ((c = fgetc(fp)) != EOF) {
chars++;
if (c == '\n') lines++;
if (isspace(c)) inWord = 0;
else if (!inWord) { inWord = 1; words++; }
}
fclose(fp);
printf("%ld %ld %ld\n", lines, words, chars);
c is int so EOF can be distinguished from valid bytes.
A null pointer holds NULL and points to nothing; dereferencing it crashes. A dangling pointer points to memory that has been freed or a local that went out of scope. A wild pointer is uninitialised and holds a random address. A void pointer is a generic pointer that can hold any object address but must be cast before dereferencing, as malloc returns void *.
A memory leak happens when dynamically allocated memory is never freed and the last pointer to it is lost, so the program keeps growing in memory use. Long running services and embedded systems eventually fail. Detect leaks with Valgrind memcheck, AddressSanitizer with LeakSanitizer or allocation tracking wrappers. Prevent them with clear ownership rules and a single cleanup path per function.
26
How do you keep improving your DSA skills while working full time?
Situation: after joining a services company I had little time for practice. Task: stay ready for product company interviews. Action: I set a goal of five problems a week on weekday mornings, joined weekend contests and kept a notebook of patterns and mistakes, revising it monthly. Result: within a year I reached a solid contest rating and cleared interviews for a backend role.
27
A doubly linked list delete function leaves the list broken when deleting the head. What is missing?
When deleting the head there is no previous node, so the head pointer itself must move to head->next, and the new head's prev must be set to NULL. Similarly, deleting the tail needs the new tail's next set to NULL. The fix is to check node->prev and node->next for NULL and update head or tail pointers accordingly, or use a sentinel node to avoid these cases.
28
Your program sorts 1 crore integers in the range 0 to 999 and qsort is too slow. What would you do?
With a small known range, use counting sort: count occurrences in an array of 1000 counters, then rewrite the array in order. It runs in O(n + k) time with only 1000 extra integers, far faster than O(n log n) comparison sorts. For larger ranges, radix sort on bytes works well. qsort also pays a function call per comparison through its comparator pointer.
29
Find the lowest common ancestor of two nodes in a binary search tree.
Use the BST order to walk down from the root.
TNode *lcaBST(TNode *root, int a, int b) {
while (root) {
if (a < root->key && b < root->key) root = root->left;
else if (a > root->key && b > root->key) root = root->right;
else return root;
}
return NULL;
}
The first node where a and b split is the LCA. Time O(h) and space O(1).
30
Find the length of the longest substring without repeating characters in C.
Sliding window with last seen positions.
int longestUnique(const char *s) {
int last[256];
for (int i = 0; i < 256; i++) last[i] = -1;
int best = 0, start = 0;
for (int i = 0; s[i]; i++) {
unsigned char c = s[i];
if (last[c] >= start) start = last[c] + 1;
last[c] = i;
if (i - start + 1 > best) best = i - start + 1;
}
return best;
}
For abcabcbb it returns 3.
Tips to crack the Qualcomm C Programming with DSA interview
Revise C programming, pointers, operating systems and computer architecture for embedded software roles.
Learn basics of wireless communication like 4G and 5G, and what a system-on-chip does.
Read about Snapdragon platforms and Qualcomm's work in automotive and AI PCs.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; Qualcomm interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Qualcomm C Programming with DSA interview?
Candidates usually go through 5 stages: Online assessment (aptitude + technical + coding); Technical round 1; Technical round 2; Managerial round; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the Qualcomm C Programming with DSA interview?
This practice set leans on Stacks, Queues and Hashing (7), Trees and Graphs (6), Pointers and Memory Management (4), Arrays and Strings (3). Revise those first, then practise explaining one or two of your own projects end to end, because most Qualcomm interviewers ask you to walk through real work.
Are these the exact questions asked at Qualcomm?
No. These are curated practice questions that match the skills and difficulty usually tested in hardware & semiconductors interviews like Qualcomm's. They are not a leaked or verified list of past questions.
Where does Qualcomm hire C Programming with DSA professionals in India?
Qualcomm has large teams in Hyderabad, Bengaluru, Chennai. Openings and locations change often, so check the Qualcomm careers page and filter by city and experience.
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