[100%] Triangle (codility lessons)

Last updated at 2021-09-29Posted at 2021-09-27

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Triangle

Determine whether a triangle can be built from a given set of edges.

Task description

An array A consisting of N integers is given. A triplet (P, Q, R) is triangular if 0 ≤ P < Q < R < N and:

A[P] + A[Q] > A[R],
A[Q] + A[R] > A[P],
A[R] + A[P] > A[Q].

For example, consider array A such that:

A[0] = 10    A[1] = 2    A[2] = 5
A[3] = 1     A[4] = 8    A[5] = 20

Triplet (0, 2, 4) is triangular.

Write a function:

class Solution { public int solution(int[] A); }

that, given an array A consisting of N integers, returns 1 if there exists a triangular triplet for this array and returns 0 otherwise.

For example, given array A such that:

A[0] = 10    A[1] = 2    A[2] = 5
A[3] = 1     A[4] = 8    A[5] = 20

the function should return 1, as explained above. Given array A such that:

A[0] = 10    A[1] = 50    A[2] = 5
A[3] = 1

the function should return 0.

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 [−2,147,483,648..2,147,483,647].

Code walkthrough

class Solution {
    public int solution(int[] A) {
        java.util.Arrays.sort(A);
        for (int i = 2; i < A.length; i++) {
            if ((long)A[i - 2] + A[i - 1] > A[i]) {
                return 1;
            }
        }
        return 0;
    }
}

Detected time complexity:

O(N * log(N))

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