二分查找法及其扩展

二分查找法源代码：

#include<iostream>
using namespace std;
int binarySearch(int arr[],int len,int goal)
{
	int high = len - 1;
	int low = 0;
	int mid = 0;
	while (high >=low)
	{
		mid = (high - low)/2 + low;
		if (goal > arr[mid])
		{
			low = mid + 1;
		}
		else if (goal < arr[mid])
		{
			high = mid - 1;
		}
		else
		{
			return mid;
		}
	}
	return -1;
}
int main()
{
	int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
	int goal;
	int len = sizeof(arr) / sizeof(arr[0]);
	cin >> goal;
	int res=binarySearch(arr,len,goal);
	cout << res << endl;
	system("pause");
}

在一个非递减有序数组，从左向右旋转之后得到的数组中，查找最小的值，如[0,1,1,1,1,1]->[1,1,1,1,0,1];最小值为0；

在递增时使用二分查找，但是在上例情况下只能遍历查找->详解见剑指offer

#include<iostream>
using namespace std;
int MiniOrder(int *arr, int low, int high)
{
	int res = arr[low];
	for (int i = low + 1; i <= high; i++)
	{
		if (res > arr[i])
		{
			res = arr[i];
		}
	}
	return res;
}
int findmin(int arr[], int len)
{
	int high = len - 1;
	int low = 0;
	int mid=0;
	while (arr[high] <= arr[low])
	{
		
		if (high - low == 1)
		{
			mid = high;
			break;
		}
		mid = (high +low)/2;
		if (arr[low] == arr[high] && arr[mid] == arr[low])
		{
			return MiniOrder(arr, low, high);
		}
		if (arr[low] <= arr[mid])
		{
			low = mid;
		}
		else if (arr[low] >arr[mid])
		{
			high = mid;
		}
	}
	return arr[mid];
}
int main()
{
	int arr[] = {1,1,1,1,0,1 };
	int len = sizeof(arr) / sizeof(arr[0]);
	int res=findmin(arr, len);
	cout << res << endl;
	system("pause");

}