06. Sorting. Triangle.swift

import Foundation
import Glibc

// Solution @ Sergey Leschev, Belarusian State University

// 06. Sorting. Triangle.

// 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].

public func solution(_ A: inout [Int]) -> Int {
    let count = A.count
    if count < 3 { return 0 }
    let sorted = A.sorted()
        
    for i in 0...count - 3 where sorted[i] + sorted[i + 1] > sorted[i + 2] { return 1 }        
    return 0
}