Finding a pair of numbers with zero sum in an array

Implement the function findTwo that takes an array of integers and returns the indices of two elements whose sum is zero.

 // findTwo([1, 2, 3, -1])    // [0, 3]
// findTwo([1, 2, 3, -1, -2, 0])    // [1, 4] or [0, 3]
// findTwo([1, 2, 3, 4])    // null