LeetCode: Search in Rotated Sorted Array

Tingmei

于 2012-10-09 00:10:04 发布

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分类专栏：算法 C++

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本文介绍了一种在旋转排序数组中查找目标值的高效算法。该算法利用二分查找的思想，在O(log n)的时间复杂度内完成搜索。文章通过一个具体的C++实现示例，展示了如何判断旋转边界并据此调整搜索范围。

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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.

class Solution {
public:
    int search(int A[], int n, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (n == 0) return -1;
        
        int l = 0;
        int u = n-1;
        while(l <= u)
        {
            int mid = l+(u-l)/2;
            
            if (A[mid] == target)
                return mid;
            else if (A[mid] > A[u])
            {
                if (A[l] <= target && target < A[mid])
                {
                    u = mid - 1;
                }
                else
                {
                    l = mid + 1;
                }
            }
            else
            {
                if (A[u] >= target && target > A[mid])
                {
                    l = mid + 1;
                }
                else
                {
                    u = mid - 1;
                }
            }
        }
        return -1;
    }
};