二分查找算法

#include <iostream>using namespace std;//假设arr都是升序//int arr[9]={1,1,1,1,1,1,1,1,1};int arr[9] ={0,0,1,1,1,3,4,4,5};/*给定一个有序（不降序）数组arr，求最小的i使得arr[i]等于v,不存在返回-1*/int BiSearch1(int s ,int e,int v ){ if(s > e) return -1; while( s < e-1 ){ int mid = s + (e-s)/2;　//防止溢出 if(v <= arr[mid] ) e = mid; //要最小的i,则整个区间要往左移 else s = mid; } if(arr[s]==v) //要最小的i,则先判断最小的下标是否满足 return s; else if(arr[e]==v) return e; else return -1;}/*给定一个有序（不降序）数组arr，求最大的i使得arr[i]等于v,不存在返回-1*/int BiSearch2(int s,int e,int v){ if(s > e) return -1; while(s < e-1) { int mid = s + (e-s)/2; if(v >= arr[mid]) s = mid ; //求最大的i使得arr[i]等于v,则整个区间往右移 else e = mid; } if(arr[e]==v)//先判断最大的下标是否满足 return e; else if(arr[s]==v) return s; else return -1;}/*给定一个有序（不降序）数组arr，求最大的i使得arr[i]小于v,不存在返回-1*/int BiSearch3(int s,int e,int v){ if(s > e) return -1; while(s < e-1) { int mid = s + (e-s)/2; if(v <= arr[mid]) // arr[i]小于v ,则整个区间往左移e = mid;elses = mid; } if(arr[e] < v)//先判断最大的下标是否满足 return e; else if(arr[s] < v) return s; else return -1;}/*给定一个有序（不降序）数组arr，求最小的i使得arr[i]大于v,不存在返回-1*/int BiSearch4(int s,int e,int v){ if(s > e) return -1; while(s < e-1) { int mid = s + (e-s)/2; if(v >= arr[mid]) // arr[i]大于v ,则整个区间往右移，s = mid;elsee = mid; } if(arr[s] > v)//先判断最大的下标是否满足 return s; else if(arr[e] > v) return e; else return -1;}int main(){cout<<BiSearch1(0,8,1)<<endl;cout<<BiSearch2(0,8,1)<<endl;cout<<BiSearch3(0,8,1)<<endl;cout<<BiSearch4(0,8,1)<<endl; system("pause"); return 0;}

 

 

//有一个升序数组 从任意地方把它截断，然后剪切到前面去，怎样找到原来数组的起始位置 #include <iostream>using namespace std;int BiSearchSplit(int arr[],int s,int e)//找到分界点{ while(s < e-1) { int mid = s +(e-s)*0.5; if(arr[mid] <= arr[s]&& arr[mid] <= arr[e] ) e = mid; else if(arr[mid] >= arr[s] && arr[mid] >= arr[e]) s = mid; } if(arr[s] > arr[e]) return s; else return -1;}int BiSearchValue(int arr[],int s,int e,int v)//找到值为v的下标{ while(s < e-1 ) { int mid = s+ (e-s)*0.5; if(v < arr[mid] ) e=mid; else s = mid; } if(arr[s]==v)return s; else if(arr[e]==v)return e; else return -1 ;}int main(){ int arr[]={100,101,102,103,1,2,3,4,5,6,7}; int len = sizeof(arr)/sizeof(arr[0]); int pos = BiSearchSplit(arr,0,len-1); int res = 0; int v = 101; if(pos == -1) res = BiSearchValue(arr,0,len-1,v); else if(arr[0] <= v) res = BiSearchValue(arr,0,pos,v); else res = BiSearchValue(arr,pos+1,len-1,v); cout<<res<<endl; system("pause"); return 0;}