Triangle

A zero-indexed 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 a zero-indexed 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.

Assume that:

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].
Complexity:

expected worst-case time complexity is O(N*log(N));
expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.

解答。

因为有 O(N*log(N))的要求，一般就要先sort一下。
sort 之后是从小到大的，除非reverse = True

然后我们就要到sorted array里面找到all possible i

import java.util.*;
class Solution {
    public int solution(int[] A) {
        Arrays.sort(A);
        for(int i = 0; i< A.length-2; i++){
            if(A[i] > A[i+2] - A[i+1]){//use subtraction to avoid overflow
                return 1;
            }
        }
        return 0;
    }
}