My codility test answers (python)
Recently, during interview to some company, I got tested by Codility service. And here is my performance results. Generally this is copy&paste from their email. Hope this can be helpful for others who want to see what this tests are.
This is overal performance table:
Task name | Correctness | Performance | Task score | |
1 | PtrListLen | 100 | not assessed | 100 |
2 | BugfixingLeaderSorted | 100 | not assessed | 100 |
3 | DeepestPit | 55 | 66 | 60 |
4 | CountMultiplicativePairs | 80 | 87 | 83 |
Total | 84 | N/A | 343 / 400 |
PtrListLen - problem description
A pointer is called a linked list if:
· it is an empty pointer (it is then called a terminator or an empty list); or
· it points to a structure (called a node or the head) that contains a value and a linked list (called the tail).
The length of a list is defined as the total number of nodes it contains. In particular, an empty list has length 0.
For example, consider the following linked list:
A -> B -> C -> D ->
This list contains four nodes: A, B, C and D. Node D is the last node and its tail is the terminator. The length of this list is 4.
Assume that the following declarations are given:
class IntList(object):
value = 0
next = None
Write a function:
def solution(L)
that, given a non-empty linked list L consisting of N nodes, returns its length.
For example, given list L shown in the example above, the function should return 4.
Assume that:
· N is an integer within the range [1..5,000];
· list L does not have a cycle (each non-empty pointer points to a different structure).
In your solution, focus on correctness. The performance of your solution will not be the focus of the assessment.
Copyright 2009–2015 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Tests
Score: 100 of 100
Estimated time complexity: None
Test name | Running time | Result |
example | 0.060 s | OK |
extreme_single_double | 0.044 s | OK |
three_elems | 0.044 s | OK |
twenty_elements | 0.044 s | OK |
medium | 0.044 s | OK |
medium2 | 0.044 s | OK |
1k_elements | 0.044 s | OK |
quite_long | 0.052 s | OK |
long | 0.056 s | OK |
Solution (language: Python)
# you can use print for debugging purposes, e.g. # print "this is a debug message" def solution(L): # write your code in Python 2.7 count = 0 while L: count = count + 1 L = L.next return count
BugfixingLeaderSorted - problem description
A non-empty zero-indexed array A consisting of N integers and sorted in a non-decreasing order is given. The leader of this array is the value that occurs in more than half of the elements of A.
You are given an implementation of a function:
def solution(A)
that, given a non-empty zero-indexed array A consisting of N integers, sorted in a non-decreasing order, returns the leader of array A. The function should return −1 if array A does not contain a leader.
For example, given array A consisting of ten elements such that:
A[0] = 2 A[1] = 2 A[2] = 2 A[3] = 2 A[4] = 2 A[5] = 3 A[6] = 4 A[7] = 4 A[8] = 4 A[9] = 6
the function should return −1, because the value that occurs most frequently in the array, 2, occurs five times, and 5 is not more than half of 10.
Given array A consisting of five elements such that:
A[0] = 1 A[1] = 1 A[2] = 1 A[3] = 1 A[4] = 50
the function should return 1.
Unfortunately, despite the fact that the function may return expected result for the example input, there is a bug in the implementation, which may produce incorrect results for other inputs. Find the bug and correct it. You should modify at most three lines of code.
Assume that:
· N is an integer within the range [1..100,000];
· each element of array A is an integer within the range [0..2,147,483,647];
· array A is sorted in non-decreasing order.
Complexity:
· expected worst-case time complexity is O(N);
· expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.
Copyright 2009–2015 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Tests
Score: 100 of 100
Estimated time complexity: None
Test name | Running time | Result |
example1 | 0.044 s | OK |
example2 | 0.044 s | OK |
simple1 | 0.044 s | OK |
simple2 | 0.044 s | OK |
single | 0.044 s | OK |
two_values | 0.044 s | OK |
extreme_big_values | 0.044 s | OK |
medium_1 | 0.044 s | OK |
medium_2 | 0.044 s | OK |
cyclic_sequence | 0.044 s | OK |
medium_random | 0.044 s | OK |
large | 0.104 s | OK |
large_range | 0.108 s | OK |
Solution (language: Python)
def solution(A): n = len(A) L = [-1] + A count = 0 pos = (n + 1) // 2 candidate = L[pos] for i in xrange(1, n + 1): if (L[i] == candidate): count = count + 1 if (2*count > n): return candidate return -1
DeepestPit - problem description
A non-empty zero-indexed array A consisting of N integers is given. A pit in this array is any triplet of integers (P, Q, R) such that:
· 0 ≤ P < Q < R < N;
· sequence [A[P], A[P+1], ..., A[Q]] is strictly decreasing,
i.e. A[P] > A[P+1] > ... > A[Q];· sequence A[Q], A[Q+1], ..., A[R] is strictly increasing,
i.e. A[Q] < A[Q+1] < ... < A[R].
The depth of a pit (P, Q, R) is the number min{A[P] − A[Q], A[R] − A[Q]}.
For example, consider array A consisting of 10 elements such that:
A[0] = 0 A[1] = 1 A[2] = 3 A[3] = -2 A[4] = 0 A[5] = 1 A[6] = 0 A[7] = -3 A[8] = 2 A[9] = 3
Triplet (2, 3, 4) is one of pits in this array, because sequence [A[2], A[3]] is strictly decreasing (3 > −2) and sequence [A[3], A[4]] is strictly increasing (−2 < 0). Its depth is min{A[2] − A[3], A[4] − A[3]} = 2. Triplet (2, 3, 5) is another pit with depth 3. Triplet (5, 7, 8) is yet another pit with depth 4. There is no pit in this array deeper (i.e. having depth greater) than 4.
Write a function:
def solution(A)
that, given a non-empty zero-indexed array A consisting of N integers, returns the depth of the deepest pit in array A. The function should return −1 if there are no pits in array A.
For example, consider array A consisting of 10 elements such that:
A[0] = 0 A[1] = 1 A[2] = 3 A[3] = -2 A[4] = 0 A[5] = 1 A[6] = 0 A[7] = -3 A[8] = 2 A[9] = 3
the function should return 4, as explained above.
Assume that:
· N is an integer within the range [1..1,000,000];
· each element of array A is an integer within the range [−100,000,000..100,000,000].
Complexity:
· expected worst-case time complexity is O(N);
· expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.
Copyright 2009–2015 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Tests
Score: 60 of 100
Test name | Running time | Result |
example | 0.044 s | OK |
extreme_no_pit | 0.044 s | WRONG ANSWER |
extreme_depth | 0.044 s | WRONG ANSWER |
simple1 | 0.044 s | WRONG ANSWER |
simple2 | 0.044 s | WRONG ANSWER |
user | 0.044 s | OK |
simple3 | 0.044 s | OK |
retries | 0.044 s | OK |
medium1 | 0.104 s | OK |
medium_pit | 0.044 s | OK |
large_pit_1 | 0.148 s | WRONG ANSWER |
large_pit_2 | 0.152 s | WRONG ANSWER |
big_pit_1 | 0.120 s | OK |
big_pit_2 | 0.132 s | OK |
big3_1 | 0.424 s | OK |
big3_2 | 1.336 s | OK |
Solution (language: Python)
# you can use print for debugging purposes, e.g. # print "this is a debug message" def solution(A): deepest = 0 pit = lambda p, q, r: min(A[p] - A[q], A[r] - A[q]) p = 0 r = -1 q = -1 l = len(A) for i in xrange(0, l): if q<0 and A[i]>=A[i-1]: q = i -1 if (q>=0 and r<0) and (A[i]<=A[i-1] or i+1==l): r = i-1 deepest = max(deepest, pit(p, q, r)) p = i-1 q = -1 r = -1 return deepest if deepest else -1
CountMultiplicativePairs - problem description
Zero-indexed arrays A and B consisting of N non-negative integers are given. Together, they represent N real numbers, denoted as C[0], ..., C[N−1]. Elements of A represent the integer parts and the corresponding elements of B (divided by 1,000,000) represent the fractional parts of the elements of C. More formally, A[I] and B[I] represent C[I] = A[I] + B[I] / 1,000,000.
For example, consider the following arrays A and B:
A[0] = 0 B[0] = 500,000 A[1] = 1 B[1] = 500,000 A[2] = 2 B[2] = 0 A[3] = 2 B[3] = 0 A[4] = 3 B[4] = 0 A[5] = 5 B[5] = 20,000
They represent the following real numbers:
C[0] = 0.5 C[1] = 1.5 C[2] = 2.0 C[3] = 2.0 C[4] = 3.0 C[5] = 5.02
A pair of indices (P, Q) is multiplicative if 0 ≤ P < Q < N and C[P] * C[Q] ≥ C[P] + C[Q].
The above arrays yield the following multiplicative pairs:
· (1, 4), because 1.5 * 3.0 = 4.5 ≥ 4.5 = 1.5 + 3.0,
· (1, 5), because 1.5 * 5.02 = 7.53 ≥ 6.52 = 1.5 + 5.02,
· (2, 3), because 2.0 * 2.0 = 4.0 ≥ 4.0 = 2.0 + 2.0,
· (2, 4) and (3, 4), because 2.0 * 3.0 = 6.0 ≥ 5.0 = 2.0 + 3.0.
· (2, 5) and (3, 5), because 2.0 * 5.02 = 10.04 ≥ 7.02 = 2.0 + 5.02.
· (4, 5), because 3.0 * 5.02 = 15.06 ≥ 8.02 = 3.0 + 5.02.
Write a function:
def solution(A, B)
that, given zero-indexed arrays A and B, each containing N non-negative integers, returns the number of multiplicative pairs of indices.
If the number of multiplicative pairs is greater than 1,000,000,000, the function should return 1,000,000,000.
For example, given:
A[0] = 0 B[0] = 500,000 A[1] = 1 B[1] = 500,000 A[2] = 2 B[2] = 0 A[3] = 2 B[3] = 0 A[4] = 3 B[4] = 0 A[5] = 5 B[5] = 20,000
the function should return 8, as explained above.
Assume that:
· N is an integer within the range [0..100,000];
· each element of array A is an integer within the range [0..1,000];
· each element of array B is an integer within the range [0..999,999];
· real numbers created from arrays are sorted in non-decreasing order.
Complexity:
· expected worst-case time complexity is O(N);
· expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.
Copyright 2009–2015 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Tests
Score: 83 of 100
Estimated time complexity: O(N)
Test name | Running time | Result |
example | 0.044 s | OK |
simple_diagonal | 0.052 s | OK |
simple_equality | 0.052 s | OK |
mulitple_zeros | 0.052 s | WRONG ANSWER |
extreme_empty | 0.044 s | WRONG ANSWER |
extreme_single | 0.044 s | OK |
doubles | 0.040 s | OK |
precision_small | 0.044 s | OK |
geometric_small | 0.044 s | OK |
arithmetic_small | 0.044 s | OK |
random_small | 0.044 s | OK |
geometric_medium | 0.064 s | OK |
random_medium | 0.064 s | OK |
arithmetic_medium | 0.088 s | OK |
geometric_large | 0.188 s | OK |
arithmetic_large | 0.244 s | OK |
random_large | 0.272 s | OK |
extreme_large | 0.280 s | OK |
extreme_zeros | 0.224 s | WRONG ANSWER |
Solution (language: Python)
def solution(A, B): # write your code in Python 2.7 if not len(A) or not len(B) or len(A) != len(B): return -1 # make C and filter all values <= 1 C = [A[i]+float(B[i])/1000000 for i in range(len(A)) if A[i]+float(B[i])/1000000 > 1] C.sort() result = 0 p = 0 # position l = len(C) - 1 while l > p: res = C[l] / (C[l] - 1) while (p < l and C[p] < res): p = p + 1 if p == l: break result = result + (l-p) if result > 1000000000: return 1000000000 l = l-1 return result
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