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hard
Find the maximum number of ropes that can be attached in order, without breaking any of the ropes.
Task Score
100%
Correctness
100%
Performance
100%
Task description

In a room there are N ropes and N weights. Each rope is connected to exactly one weight (at just one end), and each rope has a particular durability − the maximum weight that it can suspend.

There is also a hook, attached to the ceiling. The ropes can be attached to the hook by tying the end without the weight. The ropes can also be attached to other weights; that is, the ropes and weights can be attached to one another in a chain. A rope will break if the sum of weights connected to it, directly or indirectly, is greater than its durability.

We know the order in which we want to attach N ropes. More precisely, we know the parameters of the rope (durability and weight) and the position of each attachment. Durabilities, weights and positions are given in three arrays A, B, C of lengths N. For each I (0 ≤ I < N):

  • A[I] is the durability of the I-th rope,
  • B[I] is the weight connected to the I-th rope,
  • C[I] (such that C[I] < I) is the position to which we attach the I-th rope; if C[I] equals −1 we attach to the hook, otherwise we attach to the weight connected to the C[I]-th rope.

The goal is to find the maximum number of ropes that can be attached in the specified order without breaking any of the ropes.

Write a function:

int solution(int A[], int B[], int C[], int N);

that, given three arrays A, B, C of N integers, returns the maximum number of ropes that can be attached in a given order.

For example, given the following arrays:

A[0] = 5 B[0] = 2 C[0] = -1 A[1] = 3 B[1] = 3 C[1] = 0 A[2] = 6 B[2] = 1 C[2] = -1 A[3] = 3 B[3] = 1 C[3] = 0 A[4] = 3 B[4] = 2 C[4] = 3

the function should return 3, as if we attach a fourth rope then one rope will break, because the sum of weights is greater than its durability (2 + 3 + 1 = 6 and 6 > 5).

Given the following arrays:

A[0] = 4 B[0] = 2 C[0] = -1 A[1] = 3 B[1] = 2 C[1] = 0 A[2] = 1 B[2] = 1 C[2] = 1

the function should return 2, as if we attach a third rope then one rope will break, because the sum of weights is greater than its durability (2 + 2 + 1 = 5 and 5 > 4).

Write an efficient algorithm for the following assumptions:

  • N is an integer within the range [0..100,000];
  • each element of array A is an integer within the range [1..1,000,000];
  • each element of array B is an integer within the range [1..5,000];
  • each element of array C is an integer such that −1 ≤ C[I] < I, for each I (0 ≤ I < N).
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Solution
Programming language used C
Total time used 5 minutes
Effective time used 5 minutes
Notes
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