81. Search in Rotated Sorted Array II (中等)

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

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

The array may contain duplicates.

这种题自我感觉比较难．仍遵循二分查找的整体框架:

以 [4 5 6 7 0 1 2] 为例

while(lo < hi){
    case1: A[mid] > A[hi] 这时，看看 ta 在 4...mid 之间吗？
    case2: A[mid] < A[hi]　这时，看看 ta 在 mid...2 之间吗？
    case3: A[mid] == A[hi] 这时, hi--;
}

人家思想，自个代码:

\(O(logn)\) time, \(O(1)\) extra space.

bool search(vector<int>& A, int ta) {
	const int n = A.size();
	if (n == 0) return false; // special case
	int lo = 0, hi = n - 1;

	while (lo < hi) {
		int mid = lo + ((hi - lo) >> 1);
		if (A[mid] == ta) return true;
		if (A[mid] > A[hi]) {
			if (ta < A[mid] && ta >= A[lo]) hi = mid;
			else lo = mid + 1;
		} else if (A[mid] < A[hi]) {
			if (ta > A[mid] && ta <= A[hi]) lo = mid + 1;
			else hi = mid;
		} else hi--;
	}
	return ta == A[lo] ? true : false;
}