Search in Rotated Sorted Array
分段有序的数组，二分查找返回下标，没有返回-1
数组有序之后经过 rotated， 比如：6 1 2 3 4 5 or 5 6 7 8 1 2
思路是：
(1)nums[m] == target return m
(2)必定有一段是有序的，找到有序段：
// m to r is ordered
if(nums[m] < nums[r]){
if nums[m] <= targe <= nums[r] , then l = m + 1;
else: r = m - 1
// l to m is ordered
else
if nums[l] <= targe <= nums[m] , then r = m - 1
else left = m + 1;