[Leetcode] Search in a Rotated Sorted Array

最新推荐文章于 2024-05-03 20:14:24 发布

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本文介绍了一种在已知没有重复元素的旋转排序数组中查找特定目标值的有效算法。该算法利用了二分查找的思想，通过比较中间元素与数组两端元素的关系来决定搜索的方向。文章提供了一个C++实现示例。

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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.

考虑以下情况： 5,6,0,1,2,3,4 找零

class Solution {
public:
    int search(int A[], int n, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int left = 0;
        int right = n-1;
        int middle;
        
        while(left<=right)
        {
            middle = (left+right)/2;
            if(A[middle]==target) return middle;
            if(A[left]<=A[middle])
            {
                if(A[left]<=target && target<A[middle])
                {
                    right = middle - 1;
                }
                else
                {
                    left = middle + 1;
                }                
            }
            else
            {
                if(A[left]<=target || target<A[middle]) //思考：为何这里是或。
                {
                    right = middle - 1;
                }
                else
                {
                    left = middle + 1;
                }                
            }            
        }
        
        return -1;        
        
    }
};