[LeetCode]Search in Rotated Sorted Array

最新推荐文章于 2024-05-03 20:14:24 发布

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本文介绍了一种用于在已排序并旋转的数组中搜索目标值的算法，通过二分查找实现，巧妙地处理了边界条件，确保了在不包含重复元素的情况下找到目标值的索引或返回-1。

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Suppose a sorted array 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).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

分析：二分查找，难度在于左右边界的确定。

class Solution {
public:
	int search(int A[],int n,int target) {
		int low = 0, high = n-1;
		while (low != high){
			const int mid = low + (high - low) / 2;
			if (A[mid] == target)
				return mid;
			if (A[low] <= A[mid]){
				if (A[low]<=target && A[mid]>target){
					high = mid;
				}
				else
					low = mid+1;
			}
			else{
				if (target > A[mid] && target <= A[high]){
					low = mid+1;
				}
				else{
					high = mid;
				}
			}
		}
		return -1;
	}
};
class Solution1 {
	int binary_search(int A[], int low, int high, int target){
		while (low <= high){
			int mid = low + (high - low) / 2;
			if (A[mid] == target)
				return mid;
			else if (A[mid] < target)
				low = mid + 1;
			else
				high = mid - 1;
		}

		return -1;
	}

public:
	// assume it is an ascending array
	int search(int A[], int n, int target) {
		int low = 0, high = n - 1;

		while (low <= high){
			if (A[low] <= A[high]) // It will be satified at the end at least.
				return binary_search(A, low, high, target);

			int mid = low + (high - low) / 2;
			if (A[mid] == target)
				return mid;
			else if (A[mid] < A[low]){
				// [low, mid] is not ascending, [mid, high] is ascending
				if (target > A[mid] && target <= A[high])
					low = mid + 1;
				else
					high = mid - 1;
			}
			else{
				// [low, mid] is ascending, [mid, high] is not ascending
				if (target >= A[low] && target < A[mid])
					high = mid - 1;
				else
					low = mid + 1;
			}
		}
		return -1;
	}
};

int main(){
	Solution solution;

	{
		int a[] = { 4, 5, 6, 7, 0, 1, 2, };
		int target = 5;
		cout << solution.search(a, sizeof(a) / sizeof(a[0]), target)<<endl;
	}
	getchar();
	return 0;

}