Search in Rotated Sorted Array II leetcode java

题目：

Follow up for "Search in Rotated Sorted Array":

What if duplicates are allowed?

Would this affect the run-time complexity? How and why?

Write a function to determine if a given target is in the array.

 

题解：

     这道题与之前Search in Rotated Sorted Array类似，问题只在于存在dupilcate。那么和之前那道题的解法区别就是，不能通过比较A[mid]和边缘值来确定哪边是有序的，会出现A[mid]与边缘值相等的状态。所以，解决方法就是对于A[mid]==A[low]和A[mid]==A[high]单独处理。

     当中间值与边缘值相等时，让指向边缘值的指针分别往前移动，忽略掉这个相同点，再用之前的方法判断即可。

     这一改变增加了时间复杂度，试想一个数组有同一数字组成{1，1，1，1，1}，target=2, 那么这个算法就会将整个数组遍历，时间复杂度由O(logn)升到O(n)

 

 实现代码如下：

public boolean search(int [] A,int target){
if(A==null||A.length==0)
return false;

int low = 0;
int high = A.length-1;

while(low <= high){
int mid = (low + high)/2;
if(target < A[mid]){
if(A[mid]<A[high])//right side is sorted
high = mid - 1;//target must in left side
else if(A[mid]==A[high])//cannot tell right is sorted, move pointer high
high--;
else//left side is sorted
if(target<A[low])
low = mid + 1;
else
high = mid - 1;
}else if(target > A[mid]){
if(A[low]<A[mid])//left side is sorted
low = mid + 1;//target must in right side
else if(A[low]==A[mid])//cannot tell left is sorted, move pointer low
low++;
else//right side is sorted
if(target>A[high])
high = mid - 1;
else
low = mid + 1;
}else
return true;
}

return false;
}
Reference:http://www.cnblogs.com/springfor/p/3859525.html