코딩테스트#015 Triangle

문제

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].

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나의 풀이

import java.util.*;

class Solution {
    public int solution(int[] A) {
        
        if (A.length < 3) return 0;
        Arrays.sort(A);

        int length = A.length;
        for (int i = 0; i < length - 2; i++) {
            if ((long) A[i] + (long) A[i+1] > (long) A[i+2]) {
                return 1;
            }
        }

        return 0;
    }
}

Check 1 : 값의 범위

더하기 연산 시 값이 int의 범위를 초과할 수 있으므로 long으로 형변환 필요

Check 2 : 삼각형의 조건

수학 지식 : 삼각형을 만들기 위해서는 가장 긴 변 제외 나머지 두 변의 합이 가장 긴 변 보다 크면 됨