s0 = [1, 4, 9, 11]
s1 = [1, 4, 11, 9, 11]
s2 = [1, 3, 4, 9, 11]
-----
s3 = merge(s1, s2) = [1, 3, 4, 11, 9, 11]

var i = 0;
while (s1[i] === s2[i]) i++;