Search_in_rotated_sorted_array

1.问题描述

LeetCode：
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.

2.问题分析

使用二分查找。

3.代码

#include <iostream>
using namespace std;
class Solution
{
public:
	int search(int A[], int n, int target)
	{
		int first = 0, last = n;
		while(first != last)
		{
			int mid = first + (last - first) /2;
			if(A[mid] == target)
				return mid;
			if(A[first] <= A[mid])
			{
				if(A[first] <= target && target < A[mid])
					last = mid;
				else
					first = mid+1;
			}
			else
			{
				if(A[mid] < target && target <= A[last-1])
					first = mid+1;
				else
					last = mid;
			}				
		}
		return -1;
	}
};

//测试
int main(int argc, char* argv[])
{
	Solution A;
	int b[7] = {4, 5, 6, 7, 0, 1, 2};
	int index = A.search(b,7,0);
	cout << index << endl;
	system("pause");
	return 0;
}

4.总结

本题的关键在于二分查找时，确定边界。