leetcode 题解 || Search in Rotated Sorted Array 有关问题

leetcode 题解 || Search in Rotated Sorted Array 问题

problem:

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.

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Array Binary Search

在把一个排好序的序列旋转一次，再搜索一个给定值，考的是二分搜索的变种

thiking:

(1)利用二分搜索：经典二分搜索算法如下

int bsearch(int a[], int left, int right, int key)
     {
         if (left > right)
             return -1;
             
         int mid = left + (right - left) / 2;
         
         if (a[mid] == key)
             return mid;
         else if (a[mid] < key)
             return bsearch(a, mid + 1, right, key);
         else
             return bsearch(a, left, mid - 1, key);
     }

（2）这里把原序列进行了旋转，在判断下一个搜索区间时要稍加考量

code：

class Solution {
public:
    int search(int A[], int n, int target)
    {
        if(0 == n) return -1;
        int left = 0; 
        int right = n - 1;
        while(left <= right)
        {
            int midle = (left + right) >> 1;
            if(A[midle] == target) return midle;
            if(A[left] <= A[midle])
            {
                if(A[left] <= target && target  < A[midle])
                {
                    right = midle - 1;
                }
                else
                left = midle + 1;
            }
            else{
                if(A[midle] < target && target <= A[right])
                    left = midle + 1;
                else 
                    right = midle - 1;
            }
        }
        return -1;
    }
};

leetcode 题解 || Search in Rotated Sorted Array 有关问题

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