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");}