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

By sorting the array, we have guaranteed that P+R < Q and Q+R < P (because R is always the biggest). Now what remains, is the proof that P+Q > R, that can be found out by traversing the array. The chance to find such a combination is with three adjacent values as they provide the highest P and Q.

JavaScript

function solution(A) {
    // write your code in JavaScript (Node.js 6.4.0)
    var sumUp, sumDown; 
    for (var i=0, len = A.length; i < len; i++) { 
        sumUp =0;
        sumDown=0; 
        for (j=0; j<i; j++) { 
            sumUp += A[j];
        }

        for (k=(A.length-1); k>i; k--) { 
            sumDown += A[k]; 
        }

        if (sumUp === sumDown) { 
            return i; 
        }    
    }   
}
solution([-1, 3, -4, 5, 1, -6, 2, 1]);