Training ticket - Solution

solution.js

function intersects(A, a, b) {
    const rangeAStart = a - A[a];
    const rangeAEnd = a + A[a];    
    const rangeBStart = b - A[b];
    const rangeBEnd = b + A[b];    
    return (
        // the start of next range is included 
       rangeAStart <= rangeBStart && rangeAEnd >= rangeBStart 
       ||
       //
       // front is included in second part
       rangeAStart <= rangeBEnd && rangeAStart >= rangeBStart
    );
}

function solution(A) {
    let count = 0;
    for (let i = 0, len = A.length; i < len; i++) {
        for (let j = i + 1; j < len; j++) {
            count = intersects(A, i, j) ? count + 1 : count;
            if (count > 10000000) {
                return -1;
            }
        }
    }
    return count;
}