Merge Sorted Array

写了两段code，但他们原理相同。注意这里i可以由indexA + indexB + 1的值代替。make code more concise

Merge Two Sorted Arrays

challenge：How to optimize when one array is very large and the other is very small？

1.use binary search to find a place to insert the elments in the small array

1. use System.arrayucopyto method to copy the subarray in large array, this method may be more efficient than normal assignment.