int s1[K-1] = {a[1]- a[0], a[2] - a[1]...};
int s2[K-1] = {b[1]- a[0], b[2] - b[1]...};
int ans[K] = {a[0] + b[0]};
for (i = j = 0;i + j < k-1;)
{
if (s1[i] > s2[j]) ans[i+j+1] = ans[i+j] + s2[j++];
else if (s1[i] < s2[j]) ans[i+j+1] = ans[i+j] + s1[i++];
else ans[i+j+1] = ans[i+j+2] = ans[i+j] + s1[i++], j++;
}