Test results - Codility

Tasks Details

medium

1. NailingPlanks

Count the minimum number of nails that allow a series of planks to be nailed.

50%

100%

You are given two non-empty arrays A and B consisting of N integers. These arrays represent N planks. More precisely, A[K] is the start and B[K] the end of the K−th plank.

Next, you are given a non-empty array C consisting of M integers. This array represents M nails. More precisely, C[I] is the position where you can hammer in the I−th nail.

We say that a plank (A[K], B[K]) is nailed if there exists a nail C[I] such that A[K] ≤ C[I] ≤ B[K].

The goal is to find the minimum number of nails that must be used until all the planks are nailed. In other words, you should find a value J such that all planks will be nailed after using only the first J nails. More precisely, for every plank (A[K], B[K]) such that 0 ≤ K < N, there should exist a nail C[I] such that I < J and A[K] ≤ C[I] ≤ B[K].

For example, given arrays A, B such that:

A[0] = 1 B[0] = 4 A[1] = 4 B[1] = 5 A[2] = 5 B[2] = 9 A[3] = 8 B[3] = 10

four planks are represented: [1, 4], [4, 5], [5, 9] and [8, 10].

Given array C such that:

C[0] = 4 C[1] = 6 C[2] = 7 C[3] = 10 C[4] = 2

if we use the following nails:

0, then planks [1, 4] and [4, 5] will both be nailed.

0, 1, then planks [1, 4], [4, 5] and [5, 9] will be nailed.

0, 1, 2, then planks [1, 4], [4, 5] and [5, 9] will be nailed.

0, 1, 2, 3, then all the planks will be nailed.

Thus, four is the minimum number of nails that, used sequentially, allow all the planks to be nailed.

Write a function:

function solution(A, B, C);

that, given two non-empty arrays A and B consisting of N integers and a non-empty array C consisting of M integers, returns the minimum number of nails that, used sequentially, allow all the planks to be nailed.

If it is not possible to nail all the planks, the function should return −1.

For example, given arrays A, B, C such that:

A[0] = 1 B[0] = 4 A[1] = 4 B[1] = 5 A[2] = 5 B[2] = 9 A[3] = 8 B[3] = 10 C[0] = 4 C[1] = 6 C[2] = 7 C[3] = 10 C[4] = 2

the function should return 4, as explained above.

Write an efficient algorithm for the following assumptions:

N and M are integers within the range [1..30,000];

each element of arrays A, B and C is an integer within the range [1..2*M];

A[K] ≤ B[K].

Solution

Programming language used JavaScript

Time spent on task 34 minutes

Notes

not defined yet

Task timeline

Code: 17:40:17 UTC, js, verify, result: Failed

1 2 3 4 5 6

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A, B, C) {
    // write your code in JavaScript (Node.js 8.9.4)
}

Analysis

▶

example
example test

✘

RUNTIME ERROR
tested program terminated with exit code 1

Code: 17:41:01 UTC, js, verify, result: Passed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

function solution(A, B, C) {
  // write your code in JavaScript (Node.js 8.9.4)
  const N = A.length;
  let nailedPlankCount = 0;
  for (let i = 0; i < C.length; i++) {
    for (let j = 0; j < N; j++) {
      if (A[j] !== -1 && A[j] <= C[i] && B[j] >= C[i]) {
        nailedPlankCount++;
        if (nailedPlankCount === N) return i + 1;
        A[j] = -1;
      }
    }
  }
  return -1;
}

Analysis

▶

example
example test

✔

Code: 17:41:05 UTC, js, verify, result: Passed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

function solution(A, B, C) {
  // write your code in JavaScript (Node.js 8.9.4)
  const N = A.length;
  let nailedPlankCount = 0;
  for (let i = 0; i < C.length; i++) {
    for (let j = 0; j < N; j++) {
      if (A[j] !== -1 && A[j] <= C[i] && B[j] >= C[i]) {
        nailedPlankCount++;
        if (nailedPlankCount === N) return i + 1;
        A[j] = -1;
      }
    }
  }
  return -1;
}

Analysis

▶

example
example test

✔

Code: 17:41:07 UTC, js, final, score: 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

function solution(A, B, C) {
  // write your code in JavaScript (Node.js 8.9.4)
  const N = A.length;
  let nailedPlankCount = 0;
  for (let i = 0; i < C.length; i++) {
    for (let j = 0; j < N; j++) {
      if (A[j] !== -1 && A[j] <= C[i] && B[j] >= C[i]) {
        nailedPlankCount++;
        if (nailedPlankCount === N) return i + 1;
        A[j] = -1;
      }
    }
  }
  return -1;
}

Analysis summary

The following issues have been detected: timeout errors.

Analysis

Detected time complexity:

O((N + M) * N)

▶

example
example test

✔

▶

extreme_single
single nail and single plank

✔

▶

extreme_point
nail is a point [1, 1]

✔

▶

few_nails_in_the_same_place
few nails are in the same place

✔

▶

random_small
random sequence, length = ~100

✔

▶

random_medium
random sequence, length = ~10,000

✘

TIMEOUT ERROR
running time: 0.568 sec., time limit: 0.512 sec.

▶

random_large
random sequence, length = ~30,000

✘

TIMEOUT ERROR
running time: 2.092 sec., time limit: 0.496 sec.

▶

extreme_large_planks
all large planks, length = ~30,000

✘

TIMEOUT ERROR
running time: 1.628 sec., time limit: 0.496 sec.

▶

large_point
all planks are points, length = ~30,000

✘

TIMEOUT ERROR
Killed. Hard limit reached: 6.000 sec.