Caterpillar Interview Prep Questions

DSA 5

DSAMedium

What is the length of the longest run of consecutive integers in [100, 4, 200, 1, 3, 2], in any order?
1. 3
2. 4
3. 6
4. 2
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B. 4

1, 2, 3 and 4 are all present. Put every number in a hash set, start counting only from numbers whose predecessor is missing, and each number is visited a constant number of times: O(n).

This topic is named in a candidate’s interview report: Software engineer intern and full-time interview, 2023, on LeetCode.
DSAHard

What is the smallest positive integer missing from [3, 4, -1, 1]?
1. 5
2. 0
3. 2
4. 1
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C. 2

1, 3 and 4 are present and 2 is not. The O(n), O(1)-space method swaps each value v in 1..n to index v - 1, then the first index i holding the wrong value gives i + 1.

This topic is named in a candidate’s interview report: Software engineer intern and full-time interview, 2023, on LeetCode.
DSAEasy

Which data structure allows insertion and deletion at both ends in O(1)?
1. A stack
2. A binary search tree
3. A deque (double-ended queue)
4. A priority queue
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C. A deque (double-ended queue)

A deque supports push and pop at the front and the back. Python's collections.deque, C++'s std::deque and Java's ArrayDeque provide it, and a deque is what sliding-window maximum algorithms keep their candidates in.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.
DSAMedium

What is the largest distance (difference of indexes) between two equal elements in [3, 2, 1, 2, 1, 4, 5, 8, 6, 7, 4, 2]?
1. 10
2. 5
3. 9
4. 8
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A. 10

The 2s sit at indexes 1 and 11. Store the first index of each value in a hash map and, at every later occurrence, compare the current index minus the stored one: one pass, O(n).

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.
DSAEasy

You remove the 2nd node from the end of 1 -> 2 -> 3 -> 4 -> 5 in one pass with two pointers. What is the list after?
1. 1 -> 2 -> 3 -> 5
2. 1 -> 2 -> 4 -> 5
3. 1 -> 3 -> 4 -> 5
4. 1 -> 2 -> 3 -> 4
Show the answer

A. 1 -> 2 -> 3 -> 5

Move a fast pointer n steps ahead, then move both until fast reaches the last node: slow then sits just before the node to remove, 3 here, and slow.next = slow.next.next drops 4. A dummy node before the head handles removing the head itself.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

Python 1

PythonMedium

b is a with one extra character added and the letters shuffled. What does this print?
```
from functools import reduce

a, b = "intern", "nidtern"
print(chr(reduce(lambda x, c: x ^ ord(c), a + b, 0)))
```
1. n
2. e
3. d
4. i
Show the answer

C. d

XOR-ing every character code of both strings cancels each pair, because x ^ x = 0, even the repeated n, and leaves the code of the extra character, d. A Counter difference finds it too, with O(alphabet) extra space.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

C and C++ 2

C and C++Easy

On a typical machine with a 32-bit int, what does this print?
```
#include <stdio.h>
#include <limits.h>

int main(void) {
    printf("%d %d\n", INT_MIN, INT_MAX);
    return 0;
}
```
1. -32768 32767
2. -2147483647 2147483647
3. 0 4294967295
4. -2147483648 2147483647
Show the answer

D. -2147483648 2147483647

A 32-bit two's complement int holds -2^31 to 2^31 - 1. The C standard only promises at least 16 bits, so portable code reads INT_MIN and INT_MAX from limits.h, or uses int32_t from stdint.h when it needs an exact width.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.
C and C++Easy

What does this print?
```
#include <stdio.h>

int main(void) {
    int a[] = {10, 20, 30};
    printf("%d %d\n", *(a + 1), *a + 1);
    return 0;
}
```
1. 20 11
2. 11 11
3. 20 21
4. 11 20
Show the answer

A. 20 11

a + 1 points at the second element, so *(a + 1) is a[1], 20. In *a + 1 the * binds first: a[0] is 10, plus 1 is 11. a[i] is defined as *(a + i).

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

DBMS and SQL 1

DBMS and SQLMedium

An email column holds "rohit.k@example.com". In SQLite, what does this return?
```
SELECT SUBSTR(email, 1, INSTR(email, '@') - 1) FROM users;
```
1. rohit.k@
2. rohit
3. example.com
4. rohit.k
Show the answer

D. rohit.k

INSTR gives the 1-based position of "@", 8 here, so the substring takes the 7 characters before it. MySQL has SUBSTRING_INDEX(email, '@', 1) for the same job.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

Machine learning 1

Machine learningMedium

In TF-IDF, why is a word that appears in nearly every document given a low weight?
1. Because TF-IDF ignores word counts
2. Because TF is always 1
3. Because common words are removed before counting
4. IDF is log(N / documents containing the word), which is near 0 for such a word, so it cannot tell documents apart
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D. IDF is log(N / documents containing the word), which is near 0 for such a word, so it cannot tell documents apart

TF rewards a word that is frequent in this document; IDF discounts words frequent everywhere, like "the". Their product highlights words that are characteristic of one document, which is why TF-IDF vectors work well for search and text classification.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

Aptitude 2

AptitudeMedium

A father is three times as old as his son. In 8 years he will be two and a half times as old. In 16 years, how many times the son's age will he be?
1. 2.2
2. 2
3. 2.5
4. 1.8
Show the answer

A. 2.2

With the son at s, 3s + 8 = 2.5(s + 8), so 0.5s = 12 and s = 24, father 72. In 16 years they are 40 and 88, and 88 / 40 = 2.2.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.
AptitudeEasy

Sales fell by 80% from one year to the next, then returned to the first year's level the year after. By what percentage did they rise in that last year?
1. 80%
2. 500%
3. 400%
4. 100%
Show the answer

C. 400%

From 100 the sales drop to 20, then climb back to 100: a rise of 80 on a base of 20, which is 400%. A fall and a rise of the same percentage never cancel, because the base changes.

This topic is named in a candidate’s interview report: SDE intern on-campus interview, 2022, on Code360.

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DSA 5

What is the length of the longest run of consecutive integers in [100, 4, 200, 1, 3, 2], in any order?

What is the smallest positive integer missing from [3, 4, -1, 1]?

Which data structure allows insertion and deletion at both ends in O(1)?

What is the largest distance (difference of indexes) between two equal elements in [3, 2, 1, 2, 1, 4, 5, 8, 6, 7, 4, 2]?

You remove the 2nd node from the end of 1 -> 2 -> 3 -> 4 -> 5 in one pass with two pointers. What is the list after?

Python 1

b is a with one extra character added and the letters shuffled. What does this print?

C and C++ 2

On a typical machine with a 32-bit int, what does this print?

What does this print?

DBMS and SQL 1

An email column holds "rohit.k@example.com". In SQLite, what does this return?

Machine learning 1

In TF-IDF, why is a word that appears in nearly every document given a low weight?

Aptitude 2

A father is three times as old as his son. In 8 years he will be two and a half times as old. In 16 years, how many times the son's age will he be?

Sales fell by 80% from one year to the next, then returned to the first year's level the year after. By what percentage did they rise in that last year?

Prep for other employers